t  ’.,:  ■';  ■■.  ■/  .  •  ■■  •  i.  » 


*  *-. 


*  JUL  25 1911  *) 

Divivsion  *•  'BFZl 
Section 

\i.\2 


), 


ERRATA. 


Cover  Read  William  T.  Shepherd  instead  of  William'  Shepherd. 
Title  page  “  ‘‘  “  “  of 

Page  headings  Read  William  T.  Shepherd  instead  of  William  Shepherd. 

Page  III  line  5  “  ii  “  of  i. 

“  12  line  25  “  not  been  “  of  been  not. 

27  ‘‘  28  discriminate  “  of  discrimination. 

“  33  6  from  bottom  read  experimenters  instead  of  experiments. 

“  46  ‘‘  16  read  animal  instead  of  animals. 

“  50  “  34  “  unanalyzed  instead  of  analyzed. 

“  53  “  19  “  page  41  “  of  page  42. 

“  58  "  36  “  p.45ff-  “  ofp.  4off. 


Digitized  by  the  Internet  Archive 
in  2018  with  funding  from 
Princeton  Theological  Seminary  Library 


https://archive.org/details/somementalprocesOOshep 


Vol.  XII 
No.  5 


PSYCHOLOGICAL  REVIEW  PUBLICATIONS 


November,  1910 
Whole  No,  52 


THE 

Psychological  Monographs 


EDITED  BY 

JAMES  R.  ANGELL,  University  of  Chicago 
HOWARD  C.  WARREN,  Princeton  University  {Index) 

JOHN  B.  WATSON,  Johns  Hopkins  University  (Review)  and 
ARTHUR  H.  PIERCE,  Smith  College  (Bulletin) 


Some  Mental  Processes  of  the 
Rhesus  Monkey 

^  BY 

William  Shepherd,  Ph.D. 


From  the  Psychological  Laboratory  of  the  George  Washington  University 


THE  REVIEW  PUBLISHING  COMPANY 

41  NORTH  QUEEN  ST.,  LANCASTER,  PA. 
AND  BALTIMORE,  MD. 


WILLIAMS 


PRESS  OF 

A  WILKINS  COMPANY 
BALTIMORE 


CONTENTS. 


Introduction .  i 

Experimental .  6 

Formation  of  habits .  8 

Releasing  fastenings .  8 

Visual  discrimination .  i 

Brightness .  ii 

Color .  17 

Auditory  discrimination .  26 

Noise .  26 

Pitch .  27 

Inhibition  of  habits .  29 

Imitation .  33 

Ideation .  45 

Reasoning .  51 

Adaptive  intelligence .  S3 

Memory .  59 

General  Summary  and  Conclusions .  60 

Bibliography .  61 


4 


Introduction^ 


Though  one  of  the  newest  of  the  sciences,  comparative 
psychology,  or,  speaking  more  strictly,  animal  psychology, 
may  properly  claim  as  its  father  that  acute  observer  and  many- 
sided  Greek  scientist  and  philosopher,  Aristotle.  The  works 
of  this  pioneer  in  science  show  him  to  have  been  an  interested 
and  critical  student  of  the  mental,  as  well  as  the  more  strictly 
zoological  (morphological  and  physiological)  side  of  animal 
life,  of  which  latter  sciences  (morphology  and  physiology) 
he  is  the  acknowledged  father.  His  observations  on  the 
comparative  mental  and  moral  traits  of  man  and  the  lower 
animals,  so  striking  when  we  consider  the  data  he  had  at 
hand,  may  well  entitle  him  to  the  credit  of  being  the  founder 
of  comparative  psychology. 

Within  the  past  century,  the  evolution  and  anecdote 
schools,  represented  preeminently  by  Darwin,  Huxley,  Rom¬ 
anes,  Lubbock  and  their  co-laborers,  have  contributed  largely 
to  this  work  and  their  observations  and  critical  consid¬ 
erations  have  thrown  much  light  on  the  mental  capabilities 
of  animals.  These  men,  however,  depended  too  much  on  a 
method  we  now  believe  to  be  of  little  value  in  comparative 
psychology,  viz.,  observation  uncontrolled  by  experiment, 
and  their  critical  considerations  have  been  colored  because 
they  were  interested  chiefly  in  the  theoretical,  evolutionary 
interpretation  of  their  observations.  This  work,  however, 
has  been  invaluable  in  that  the  broader  questions  have  been 
set,  and  especially  in  that  it  has  given  great  stimulus  to  the 
study  of  the  animal  mind. 

It  has  remained  for  the  new,  the  conservative,  experi¬ 
mental,  school  of  comparative  psychology,  to  define  more 

*  The  animals  used  in  this  research  were  supplied  by  Prof.  Shepherd  Ivory  Franz, 
of  the  George  Washington  University,  through  a  grant  to  him  from  the  Carnegie 
Institution  of  Washington.  Acknowledgment  is,  therefore,  made  to  the  Carnegie 
Institution,  without  whose  aid  the  work  would  not  have  been  possible. 


2 


WILLIAM  SHEPHERD. 


accurately  the  problems  of  the  science,  and  by  more  accur¬ 
ate  observations  and  by  carefully  controlled  experiments  to 
solve  those  problems.  To  this  more  scientific  and  growing 
body  of  workers,  to  Morgan  and  Hobhouse  in  England,  to 
Forel,  Bethe  and  Hatchet-Suplet  on  the  Continent,  and  to 
Mills,  Thorndike,  Yerkes  and  Watson  in  America,  must  be 
paid  the  highest  tribute. 

As  results  of  the  first  part  of  the  work  of  this  newer  school 
distinct  problems  have  been  more  precisely  formulated  by  the 
investigators.  These  problems  may  be  divided  into  two 
general  classes,  each  of  which  may  be  resolved  into  a  number 
of  concrete  special  problems.  The  first  general  problem  is: 
Do  animals  possess  the  lower  mental  powers  that  man  pos¬ 
sesses?  Do  they  have  the  same  fundamental  psychic  states 
that  man  has;  and,  if  so,  how  do  these  states  differ  qualita¬ 
tively  and  quantitatively  from  those  of  man?  To  be  more 
concrete,  we  may  ask:  Do  the  lower  animals  discriminate 
sensory  qualities,  do  they  discriminate  brightness  of  lights, 
do  they  discriminate  colors  or  hues,  noises,  smells,  and  tactile 
stimuli?  Do  they  form  and  inhibit  habits,  do  they  retain 
impressions  and  have  the  elements  of  memory?  In  what 
way,  if  at  all,  do  these  differ  from  similar  mental  powers  of 
man?  The  second  general  problem  is:  Do  the  lower  animals 
have  the  so-called  higher  powers?  Have  they  ideas,  have 
they  the  ability  to  learn  by  imitation,  have  they  general 
notions  and  reason?  From  any  psychological  considera¬ 
tion  we  may  omit  the  question  of  the  presence  of  moral 
judgments,  a  subject  which  is  chiefly  of  ethical  and  religious 
interest. 

Despite  both  the  newness  and  the  difficulties  of  the  prob¬ 
lems  and  the  imperfections  of  many  of  the  present  experi¬ 
mental  methods  of  study  in  this  field,  much  work  has  been 
accomplished  and  many  valuable  results  have  been  obtained. 
The  results  are,  however,  yet  too  few,  and  some  of  those  of 
more  general  interest  have  led  to  unsettled  controversies. 
Some  of  the  results  which  at  present  may  be  considered 
established  are  as  follows:  Some  animals,  the  higher  forms 
at  least,  discriminate  brightness  values.  Some  classes  of 


INTRODUCTION. 


3 


animals  discriminate  pitch.  All  vertebrates  and  some  in¬ 
vertebrates  show  an  ability  to  form  habits  of  reaction  to 
stimuli,  and  they  form  at  least  simple  associations.  Animals 
retain  impressions  and  have  a  memory  of  some  sort.  Even 
the  most  conservative  and  hypercritical  have  found  this  to 
be  the  only  satisfactory  interpretation  of  the  results  of  ex¬ 
periments,  and  it  is  almost  needless  to  say  that  the  adherents 
of  the  so-called  anecdote  school  admit  a  high  degree  of  mem¬ 
ory  in  all  mammalia. 

The  question  on  which  comparative  psychologists  are 
divided  are  as  numerous  as  may  be  expected  in  a  growing 
science.  Those  of  most  interest  in  connection  with  the 
present  study  may  be  briefly  mentioned.  Have  animals 
the  same  sensory  equipment  as  man?  Have  animals  color 
vision?  Or,  do  they  merely  appear  to  discriminate  colors 
because  of  differences  in  the  brightness  values  of  the  stimuli 
that  are  used?  Do  animals  learn  by  inferential  imitation? 
Have  the  lower  animals  ideas  or  mental  images? 

In  answer  to  these  questions  animal  psychologists  have 
arrived  at  directly  opposite  conclusions,  although  all  the 
recent  investigators  believe  they  follow  the  law  of  parsimony 
enunciated  by  Lloyd  Morgan.  In  regard  to  the  so-called 
higher  mental  powers,  recent  experimenters  have  taken  a 
less  decided  stand  than  formerly.  They  cease  to  deny  to 
animals  reason,  imitation  and  other  similarly  complex  proc¬ 
esses,  but  they  say  the  case  is  not  proven  and  demand 
additional  experiments  and  observations. 

Among  experimenters  on  animals  Hobhouse  is  almost 
alone  in  claiming  that  animals  have  true  general  notions. 
It  is  true  he  does  this  after  having  made  rather  important 
qualifications  of  the  term  ‘idea.’  The  latter  topic  has,  how¬ 
ever,  not  been  the  subject  of  many  experiments  or,  rather, 
it  has  not  been  the  subject  of  many  reported  experiments 
and  observations  other  than  a  few  illy-controlled  ones.  The 
question  of  the  ability  of  animals  to  reason  has  been  the 
subject  of  numerous  tests;  but  the  casual  observations  of 
the  anecdote  psychologists  are  the  mainstay  of  those  who 
support  the  view  that  animals  show  ability  to  reason.  Hob- 


4 


WILLIAM  SHEPHERD. 


house  has  made  some  experiments  which  he  believes  indicate 
some  power  or  inference  in  monkeys  and  apes,  but  the  obser¬ 
vations  that  have  been  made  by  others  of  the  group  of 
experimental  animal  psychologists  are  in  the  main  of  a  de¬ 
cidedly  negative  character.  With  the  exception  of  Hob- 
house,  it  may  be  said  that  the  consensus  of  opinion  is  that 
the  presence  in  animals  of  this  so-called  higher  faculty  is  not 
proven. 

These  points  we  may  summarize  by  saying  that  at  present 
comparative  psychologists  admit  the  possession  by  animals 
of  most  of  the  lower  powers  of  intelligence  that  man  possesses. 
Such  powers  of  animals  may,  however,  differ  from  those  of 
man  quantitatively  and  in  a  qualitative  manner.  Possession 
by  animals  of  the  so-called  higher  powers  is  an  open  question, 
or  set  of  questions,  which  have  not  been  so  widely  studied,  nor 
so  clearly  determined;  and,  respecting  which  the  available 
evidence  points  toward  a  negative  answer  in  the  form  of  a 
verdict  of  ‘Not  proven,’ 

On  account  of  the  ease  of  obtaining  the  domesticated 
animals  a  large  amount  of  the  experimental  work  on  animal 
behavior  has  been  performed  upon  cats,  dogs  and  chicks. 
On  the  other  hand,  the  lower  forms  (invertebrates  and  non¬ 
mammalian  vertebrates)  have  been  extensively  studied  in 
respect  to  the  simplest  powers,  such  as  tropisms.  On  account 
of  expense,  difficulties  of  care  and  the  apparent  complexity 
and  variety  of  behavior,  the  higher  mammalian  types,  especi¬ 
ally  anthropoids,  have  not  been  studied  so  consistently. 

However,  for  studies  in  comparative  psychology  the  value 
of  using  primates  instead  of  the  lower  vertebrates  and  inverte¬ 
brates  is  almost  self-evident.  On  the  one  hand,  the  anatomi¬ 
cal  similarities  between  man  and  the  monkey  are  apparent. 
There  is  the  well-known  similarity  between  both  their  peripheral 
and  central  nervous  systems;  and  the  similarity  of  arrange¬ 
ment  of  muscles  and  bones,  especially  of  the  extremities, 
must  not  be  forgotten.  Observations  have  made  it  evident 
that  there  are  also  similarities  in  a  physiological  way.  Move¬ 
ments  and  reactions  of  an  apparently  human  type  are  known 
to  be  present  in  these  higher  forms,  which  are  difficult  if  not 


INTRODUCTION. 


5 


impossible  to  observe  in  the  lower  forms.  We  may  there¬ 
fore  expect  from  the  careful  studies  of  the  mental  states  of 
those  animals,  admitted  to  be  immediately  inferior  to  that 
of  man,  more  light  on  certain  problems  in  the  psychology 
of  human  consciousness  than  from  similar  studies  of  others. 
In  making  such  a  comparison  of  values  it  is  not  intended  in 
any  way  to  detract  from  or  to  belittle  the  studies  on  the  lower 
forms.  The  value  of  experiments  with  the  lower  orders  is 
everywhere  admitted.  But  at  present  it  must  also  be  ad¬ 
mitted  that  the  latter  have  received  the  attention  of  many 
more  writers,  and  their  reactions  have  been  subjected  to  a 
much  finer  analysis. 


Experimental 


The  brief  historical  summary  of  comparative  psychology 
which  we  have  given  will,  perhaps,  appear  as  a  sufficient 
justification  for  undertaking  further  study  in  the  field;  both 
in  regard  to  the  lower  and  to  the  higher  faculties  in  the  animal 
mind.  This  study  of  the  psychology  of  monkeys  was  under¬ 
taken,  therefore,  with  a  view  to  add  to  the  knowledge  we 
now  possess  of  the  lower  faculties  in  the  animal  mind,  and  if 
possible,  to  throw  some  light  upon  the  question  of  whether 
or  not  monkeys  possess  some  of  the  higher  mental  powers, 
and  also  to  limit  or  characterize  any  such  higher  powers,  if 
they  should  be  found.  The  experiments  have  been  much  too 
incomplete  to  be  entirely  satisfactory  to  me,  and,  in  many 
cases,  the  results  are  naturally  lacking  in  definite  conclusions, 
though  they  yielded,  to  me  at  least,  some  valuable  indica¬ 
tions  in  the  field.  It  must  be  said,  however,  that  the  unsatis¬ 
factoriness  and  the  indefiniteness  are  not  peculiar  to  this 
particular  study,  but  that  they  apply  to  any  work  that  is 
performed  in  such  a  complex  science.  In  certain  of  the  later 
experiments,  it  will  be  noted,  definite  conclusions  have  been 
arrived  at,  and,  had  time  permitted  the  carrying  out  of 
further  experiments,  it  seems  probable  that  other  tests  might 
have  been  concluded  in  as  definite  a  way. 

As  tests  of  some  of  the  so-called  lower  faculties  of  the 
monkey’s  intelligence,  experiments  were  made  on  brightness 
discrimination,  color  discrimination,  auditory  discrimination, 
the  formation  and  inhibition  of  habits,  and  retentive  power 
(memory).  In  regard  to  the  higher  powers,  observations 
and  experiments  were  made  on  learning  by  imitation,  on 
ideation,  on  reasoning,  on  adaptive  intelligence  and  on 
general  notions.  In  brief,  the  chief  aim  of  the  study  has 
been,  while  profiting  by  the  work  of  preceding  investigators, 
and  with  a  steady  adherence  to  the  law  of  parsimony,  to  study 
some  of  the  lower  powers  of  the  animal  mind,  but  especially 


EXPERIMENTAL. 


7 


by  a  modest  study  of  the  higher  powers  to  seek  for  some 
light,  however  little,  on  the  subject  of  mental  evolution. 
Eleven  monkeys  were  used  in  this  work.  All  were  Rhesus 
(Macacus)  obtained  soon  after  their  importation  from  India. 
So  far  as  we  could  ascertain  they  were  eight  to  nine  months 
old  when  received  and,  with  the  possible  exception  of  monkey 
2,  they  appeared  to  be  without  training  of  any  kind.  Monkey 
I  was  a  rather  large,  spare  male,  moderately  active  and  bright 
looking;  in  his  work  he  showed  only  medium  capacity; 
when  he  could  not  perform  an  act  and  thus  get  food  he  showed 
signs  of  anger,  by  jumping  about  and  by  shaking  the  wire 
sides  of  the  cage;  he  would  sometimes  jump  at  the  experi¬ 
menter  and  visitors  who  happened  to  be  in  the  room,  but  it 
must  be  remembered  he  was  in  a  cage  and  could  not  get  at 
anyone;  the  movements  he  made  were  those  of  intimidation, 
so  often  noticed  in  the  Rhesus  and  other  Macacque  monkeys; 
towards  the  end  of  the  series  of  experiments  he  became 
cross.  Monkey  2  was  a  medium-sized  male;  moderately 
active  and  of  only  ordinarily  intelligent  appearance;  he 
showed  a  mediocre  capacity  in  work;  not  friendly;  he  wore 
a  collar  about  his  neck  when  received  and  this  would  indicate 
that  he  may  have  been  accustomed  to  handling  by  sailors 
or  by  others  who  previously  owned  him.  Monkey  3  was  a 
small  female,  apparently  the  youngest  of  the  eleven,  very 
active,  alert;  good-natured  and  friendly  for  a  Rhesus;  formed 
associations  the  quickest  of  all  the  animals.  Monkey  4 
was  a  medium-sized  male,  not  very  active,  but  bright  and 
cunning  looking;  good-natured;  jumped  at  experimenter 
half  playfully;  of  medium  capability  in  his  work.  Monkey 

5  was  a  large  male,  dull  looking,  not  active;  slow  in  learning 
as  compared  with  all  the  others;  he  had  a  way  of  whining  when 
left  alone;  was  rather  ill-natured;  would  get  angry  when  he 
failed  to  do  a  required  act,  and  thus  fail  to  get  food.  Monkey 

6  was  a  small  female;  bright  and  active;  good-natured;  very 
cautious  in  all  her  work  and  actions.  Monkey  7  was  a  large 
female;  inactive,  not  very  bright  looking,  but  the  most 
friendly  of  the  eleven  animals;  proved  to  be  quick  in  forming 
habits;  very  quiet.  Monkey  8  was  a  large  male;  he  was  the 


8 


WILLIAM  SHEPHERD. 


master  of  the  band;  of  gruff  appearance,  domineering,  active; 
of  not  especially  intelligent  appearance;  but  was  extremely 
cautious,  appeared  to  like  to  go  through  the  tests.  Monkey 
9  was  a  medium  large  female;  rather  friendly;  quick  to  form 
habits.  Monkey  lo  was  a  large  female;  not  active;  quite 
friendly;  fairly  capable  as  indicated  in  the  tests.  Monkey 
II  was  a  large  male;  wise  looking;  quiet  and  friendly;  some¬ 
what  timid;  of  medium  capability. 

Formation  of  habits. 

Releasing  fastenings:  Since  the  appearance  of  Thorndike’s 
Animal  Intelligence  in  1898  the  puzzle  box  method  has  been 
a  favorite  one  for  comparative  psychologists  in  studying  the 
formation  of  associations’  by  the  mammalia.  Partly  as  pre¬ 
liminary  to  succeeding  work  on  visual  discrimination,  an 
experiment  similar  to  those  of  Thorndike  was  made  with 
monkeys  i,  2  and  3. 

A  box  2  feet  long,  7  inches  wide  and  8  inches  deep  was  made 
with  wooden  slats  and  attached  to  one  end  of  the  cage  in 
which  the  three  animals  were  kept.  A  solid  wooden  door, 
6  by  4  inches,  was  arranged  on  each  side  of  the  inner  or  parti¬ 
tion  part  of  this  box  nearest  to  the  cage.  These  doors  had 
vertical  hinges  and  were  kept  shut  by  a  turn  button  on  the 
side  away  from  the  animals.  The  hinged  portions  were  16 
inches,  the  opening  or  button  portions  8  inches  apart.  A 
space  was  left  on  the  sides  of  the  doors  next  to  the  button 
sufficiently  wide  to  enable  a  monkey  to  put  his  hand  through. 
The  doors  opened  inward  into  the  feed  box,  i.e.,  outward 
from  the  monkey  cage.  The  food  was  usually  so  placed  on 
the  floor  of  the  food  box  that  the  animal  could  not  see  it, 
except  by  going  to  the  extreme  right  or  left,  depending  upon 

1  The  term  ‘  association’  as  applied  to  the  intelligence  of  animals  has  been  loosely 
used.  Two  principal  usages  are:  (o)  the  animal’s  simple  cerebral  (or  mental)  processes 
(merely  anatomical,  or  it  may  be,  physiological)  such  as  is  shown  in  a  simple  adjust¬ 
ment  to  a  stimulus,  e.g.,  in  its  learning  to  turn  a  button  to  open  a  door;  {h)  as  explain¬ 
ing  what  are  thought  by  some  psychologists  to  be  higher  mental  processes,  e.g.,  idea¬ 
tion  or  reasoning.  When  used  in  this  paper  the  word  is  to  be  understood  to  have  a 
connotation  similar  to  the  first  meaning  given  above. 


RELEASING  FASTENINGS. 


9 


the  box  into  which  the  food  was  placed.  In  all  experiments, 
even  in  those  in  which  no  time  is  recorded  in  the  paper,  the 
times  for  the  performance  of  acts  were  taken  by  a  stop  watch 
and  recorded. 

By  reaching  through  the  space  or  crack  at  the  side  of  the 
door  and  turning  the  button,  the  monkey  could  open  the  door 
and  secure  the  food  which  was  placed  in  the  food  box  behind 
one  of  the  doors.  In  the  beginning  of  the  work  only  one  of 
the  doors  was  used ;  when  the  association  of  turning  the 
button,  i.e.,  of  opening  one  door,  was  formed,  both  doors  were 
used.  In  the  latter  (two-door)  preliminary  experiments  the 
food  was  placed  in  a  chance  order  behind  one  of  the  doors, 
the  animal  not  knowing  which  door  that  might  be. 

The  records  of  the  three  animals  used  in  this  first  experi¬ 
ment  are  as  follows:  On  the  fourth  day,  after  32  trials, 
monkey  i  gave  evidence  of  the  formation  of  the  habit  of 
opening  the  door.  Previous  to  this  trial  he  had  shown 
many  random  movements,  going  from  one  part  of  the  cage 
to  another,  getting  upon  a  bench  in  the  cage,  stopping  all 
work  for  a  time,  etc.  On  the  fourth  day,  however,  the  habit 
of  going  to  the  door  directly  was  apparently  formed,  and  the 
method  of  opening  was  that  of  vigorously  shaking  the  door 
so  that  the  button  was  gradually  moved  to  permit  the  open¬ 
ing  of  the  door.  On  the  fifth  day,  after  53  trials  in  all,  he 
began  to  fumble  with  the  button  in  addition  to  shaking  the 
door.  He  continued  to  use  both  of  these  means  with  an 
increasing  tendency  to  rely  on  the  button  alone.  On  the 
sixth  day,  after  95  trials  in  all,  he  had  formed  the  association 
of  opening  the  doors  by  turning  the  buttons  alone.  His 
average  time  for  10  succeeding  trials  on  this  day  was  3  seconds. 
Monkey  2  formed  the  association  of  opening  the  door  in  much 
the  same  manner  as  Monkey  i.  He  pulled  and  shook  it, 
and  on  the  third  day,  after  21  trials  in  all,  managed  to  get 
the  trick  of  always  opening  it  in  this  manner.  On  the  fourth 
day,  after  51  trials  in  all,  he  began  to  turn  the  button  in 
addition  to  pulling  and  shaking  the  door.  Also  similarly 
to  the  actions  of  Number  i,  he  continued  to  use  one  or  both 
of  the  means,  with  an  increasing  tendency  to  turn  the  button 


lO 


WILLIAM  SHEPHERD. 


alone.  On  the  sixth  day,  after  102  trials,  he  always  used  the 
button  alone  as  the  means  of  opening  the  door.  His  average 
time  for  ten  successive  trials  was  1.5  seconds.  Number  3 
on  the  second  day,  and  after  ii  trials  in  all,  formed  the  asso¬ 
ciation  of  opening  the  door  by  pulling  and  pressing  it.  On 
the  third  day,  after  34  trials  in  all,  she  began  to  turn  the 
button.  On  the  fourth  day,  after  64  trials  in  all,  she  appeared 
to  have  perfected  the  latter  association  and  had  inhibited 
all  tendency  to  use  other  means  {e.g.,  shaking)  for  opening 
the  door.  Her  average  time  in  the  last  10  successive  trials 
on  this  day  was  approximtaely  1.5  seconds. 

The  method  of  learning  in  this  experiment  appeared  to  be 
of  the  Trial  and  error’  type.  As  has  been  mentioned,  the 
animals  scrambled  about  in  a  general  way  at  first;  they  pulled 
and  bit  at  the  door  and  the  adjacent  parts  of  the  partition; 
shook  the  door  violently;  but,  it  is  to  he  noted  that  after  the 
first  few  experiments  the  attention  of  the  animal  was  always 
directed  to  the  door.  Even  after  an  accidental  success  in 
turning  the  button,  the  association  was  not  at  once  set,  but 
only  after  a  number  of  trials,  with  accidental  successes  many 
times  repeated,  alternating,  or  rather  interspersed,  with  many 
errors.  All  the  animals  used  in  this  work  appeared,  however, 
to  recognize  a  chance  success  and  profited  by  it  more  quickly 
than  did  raccoons  under  similar  conditions.  Another  thing 
of  particular  notice  in  their  work,  in  which  respect  also  they 
differed  from  the  raccoons,  was  their  tendency  to  show  signs 
of  anger  when  they  could  not  open  the  door  and  get  the 
desired  food.  This  was  especially  noticeable  with  Monkey  i. 

It  is  also  of  interest  to  note  that  when,  preparatory  to  an¬ 
other  trial,  I  attempted  to  close  the  door  after  an  animal 
had  opened  the  door  and  obtained  food,  the  animal  would 
repeatedly  attempt  to  hold  the  door  open,  as  if  the  idea  was 
present  that  ‘door-being-open’  meant  food.  This  reaction 
is  somewhat  similar,  I  judge,  to  one  observed  by  Thorndike 
in  his  experiments  with  cats.  It  will  be  remembered  this 
author  found  a  tendency  on  the  part  of  the  animals  to  walk 
into  the  opened  cage  from  which  they  had  just  previously 
escaped  to  obtain  food.  The  action,  on  the  other  hand,  may 
be  merely  of  the  nature  of  a  reflex. 


VISUAL  DISCRIMINATION. 


II 


Visual  discrimination.  It  was  formerly  supposed,  or  rather 
taken  for  granted,  that  animals  possess  the  power  of  dis¬ 
crimination  of  visual  qualities,  hues,  and  saturations.  This 
assumption  was  based  upon  observations  of  general  be¬ 
havior,  of  reactions  to  objects  of  different  color,  etc.,  but 
in  the  past  few  years,  however,  comparative  psychologists 
have  concluded  that  such  power  of  discrimination  could  not 
be  assumed  and  they  have  sought  by  carefully  controlled 
experiments  to  test  the  truth  of  the  matter.  While  the 
experiments  already  made  have  yielded  many  valuable  and 
apparently  positive  results,  several  investigators,  among 
whom  may  be  mentioned  Yerkes  (4)  and  Watson  (2), 
await  more  proof  of  such  discrimination  ability.  The  prob¬ 
lem  has  been  resolved  into  two  questions.  Is  there  a  dis¬ 
crimination  by  animals  of  brightnesses  or  intensities?  Do 
animals  discriminate  objects  by  their  color  or  hue  qualities? 
In  the  work  on  visual  discrimination  to  be  recorded  in  this 
paper  nine  monkeys  were  tested  for  color  discrimination  and 
six  for  brightness  (or  intensity)  discrimination. 

Brightness  Discrimination — Simultaneous  Expos¬ 
ures:  Some  experiments  on  monkeys  i,  2,  and  3  were  made 
with  the  same  apparatus  that  was  employed  in  the  prelimin¬ 
ary  experiments  on  the  releasing  of  fastenings,  with  the  addi¬ 
tion  of  two  cards,  respectively  black  and  white,  which  were 
placed  above  the  doors.  The  cards  were  5  inches  square, 
and  were  placed  above  the  doors.  They  were,  therefore,  8 
inches  apart.  A  piece  of  food,  usually  a  half  or  a  whole  pea¬ 
nut  was  dropped  in  the  food  box;  the  black  card  was  placed 
above  the  door  behind  which  the  food  had  been  placed,  and 
the  white  card  above  the  other  door.  The  monkey  was  to 
open  the  door  under  the  black  card  and  obtain  the  food. 
The  food  was  placed  in  the  compartments  in  an  irregular 
order,  and  the  cards  were  correspondingly  placed.  At  times 
the  food  was  not  placed  In  the  box  until  the  door  had  been 
opened  by  the  animal,  but  often  it  was  dropped  In  the  box 
immediately  before  or  after  the  buttons  were  adjusted.  In 
this  way  it  was  possible  to  prevent  the  animal  knowing  which 
door  to  open  from  the  sight  of  food,  and  since  raw  peanuts 


12 


WILLIAM  SHEPHERD. 


were  used,  the  smell  component,  judging  at  least  from  human 
ability  to  smell  such  food  was  at  a  minimum. 

These  experiments  were  begun  December  4th  and  con¬ 
tinued  for  eleven  weeks.  Each  animal  was  given  from  10 
to  25  trials  every  second  or  third  day.  In  some  cases  there 
were  longer  intervals  between  the  work  periods.  Each 
animal  was  given  a  total  of  1000  trials.  At  the  end  of  the  work 
all  were  substantially  perfect  in  opening  the  door  under  the 
black  card  first.  No  animal  was  ever  able  to  inhibit  alto¬ 
gether  the  tendency  to  open  the  door  under  the  white  card 
after  the  door  under  the  black  card  had  been  opened  and  the 
food  had  been  secured.  The  average  time  for  opening  the 
door  under  the  black  card  in  the  last  25  trials  for  these  three 
monkeys  was  approximately  one  second.  The  curves  of 
learning,  i.e.,  the  time-experiment  curves,  correspond  to 
those  found  by  almost  all  experimenters,  but  on  account  of 
mistakes  in  opening  the  second  door  they  cannot  have  much 
value  in  this  connection. 

The  fact  that  the  animals  formed  the  habit  of  opening  the 
door  under  black  first  would  indicate  that  they  discriminated 
the  cards.  The  quickness  with  which  they  finally  performed 
the  act  would  also  confirm  this  conclusion.  Moreover  their 
looks  and  actions  at  the  time  appeared  to  indicate  a  knowledge 
that  the  opened  door  meant  food.  When,  for  example,  food 
had  been  not  placed  in  the  box,  after  opening  the  door  they 
would  look  at  me  as  if  they  expected  their  reward.  The 
closeness  of  the  door  buttons,  and  the  great  activity  and 
ready  use  of  the  hands,  explain,  I  believe,  the  opening  of  the 
second  door  so  often.  Furthermore,  it  was  noted  that  while 
after  they  had  opened  the  door  under  the  black  card,  they 
appeared  to  expect  food,  when  the  door  under  white  was 
opened,  their  actions  did  not  indicate  that  they  expected  to 
be  fed. 

Brightness — Successive  Exposures.  For  the  tests  with 
monkeys  4,  5,  and  6,  I  used  a  card  displayer  similar  to  that 
used  by  Professor  Cole  and  myself  in  brightness  and  color 
tests  made  on  raccoons.  This  was  placed  outside  and  about 
6  inches  from  the  animal  cage.  The  accompanying  figure 


VISUAL  DISCRIMINATION. 


13 


is  a  diagram  of  the  experimenter’s  view  of  this  piece  of  ap¬ 
paratus.  (See  Figure  i.) 

The  front  of  the  displayer  was  formed  by  a  board  12  inches 
high.  A  pin,  ‘P’,  on  which  two  levers  could  be  turned,  was 
inserted  in  a  hole  at  the  back  and  near  the  lower  edge.  On 
this  pin  two  displayers,  ‘W’  and  'B’,  were  arranged  so  as  to 
be  freely  movable  in  the  plane  of  the  board.  The  two  cards, 
black  and  white,  were  placed  at  the  upper  end  of  the  dis¬ 
players  so  that  the  raising  of  the  displayers  showed  the  black 
and  white  cards  respectively.  The  card  displayers  were 
I -inch  thick  so  that  there  was  a  difference  of  i  inch  in  the 
distances  of  the  cards  from  the  animal  box.  On  alternate 


days,  however,  the  cards  were  changed  from  the  front  to 
the  back  lever,  so  the  animals  should  not  react  merely  to  the 
distance  position  of  a  card.  When  the  black  was  exhibited 
the  animal  was  to  go  upon  a  platform  arranged  inside  the 
cage  and  was  fed,  while  he  was  not  to  go  up  at  white  and  was 
not  fed.  Usually  and  except  at  the  stimulus,  the  animal  sat 
on  a  bench  12  inches  from  the  floor  and  inside  the  cage. 
He  was,  therefore,  in  a  position  to  look  down  at  the  card 
apparatus,  for  the  upper  portion  of  the  card  was  about  5 
inches  below  the  horizontal  level  of  his  eyes.  When  the 
black  card  was  displayed  and  the  monkey  had  climbed  to  the 
food  platform  the  experimenter  rose  from  his  seat  and  pre¬ 
sented  a  piece  of  food  to  the  animal.  It  is  of  interest  to  note, 
therefore,  that  there  was  no  possibility  of  the  formation  of 
an  association  between  the  smell  of  food  and  food,  rather 


14 


WILLIAM  SHEPHERD. 


than  between  the  appearance  of  the  card  and  food.  Since 
the  food  was  not  placed  near  the  cage  or  near  the  food  plat¬ 
form  until  the  appropriate  response  was  obtained  the  animal 
had  no  smell  stimulus  for  its  guidance  to  an  appropriate 
reaction. 

These  experiments  were  begun  February  5th  and  con¬ 
tinued  for  a  period  of  seven  weeks.  Each  animal  was  given 
from  10  to  25  trials  daily,  with  intervals  of  two  days,  in  some 
cases  of  three  or  four  days,  during  which  intervals  no  work 
was  done  with  them  on  brightness.  In  all,  each  was  given 
700  trials.  At  the  close  of  this  work  monkeys  4  and  6  ap¬ 
peared  to  have  the  association  perfected.  The  average  times 
for  responding  by  going  upon  the  platform  when  black  was 
displayed  in  the  last  25  trials  were  1.5  seconds  for  monkey  4 
and  1.25  seconds  for  monkey  6.  The  tendency  to  climb  to 
the  food  platform  when  white  was  displayed  appeared  to  be 
entirely  inhibited.  Monkey  4  was,  in  this  regard,  perfect 
in  the  last  25  trials,  and  monkey  6  responded  to  white  only 
once  in  the  same  number  of  trials.  Moreover,  at  the  time 
of  this  mistake  it  was  noted  that  in  the  trial  (the  7th)  in  which 
she  responded  to  white,  monkey  6  immediately  came  down 
from  the  food  platform  with  all  the  appearance  of  having 
knowledge  that  she  had  made  a  mistake;  she  did  not  appear 
to  expect  food  and  did  not  remain  upon  the  platform  for  a 
sufficient  time  to  have  food  presented  to  her. 

Monkey  5,  at  the  end  of  the  700  tests,  appeared  to  be 
almost  perfect.  In  responding  to  black  he  made  only  one 
error  in  the  last  25  trials.  His  inhibition  of  the  tendency  to 
respond  to  white  was  not  quite  perfect,  for  during  the  same 
series  he  responded  to  the  white  card  three  times.  His 
errors  in  this  latter  regard,  however,  were  rather  of  the  type 
shown  by  monkey  6.  He  showed  by  his  actions  that  he  knew 
he  had  made  a  mistake,  for  without  waiting  to  be  fed  he 
immediately  returned  from  the  food  platform  to  the  bench. 

In  the  later  experiments,  and  probably  for  some  time 
previous  to  the  ones  just  mentioned,  the  movement  of  the 
card  displayer  appeared  to  set  up  in  the  animals  a  tendency 
to  react,  and  the  mistakes  that  were  made  on  the  last  day 


VISUAL  DISCRIMINATION. 


IS 

are,  in  my  opinion,  undoubtedly  due  to  the  lack  of  inhibition 
of  this  reflex  tendency  to  movement  rather  than  to  mistakes 
in  ability  to  discriminate. 

For  the  next  tests  in  this  series  small  pieces  (about  one- 
half  inch  cube)  of  white  and  rye  bread  were  presented  simul¬ 
taneously  on  a  board  placed  outside  the  cage  but  within  reach 
of  the  animal.  The  breads  were  prepared  so  that  the  taking 
of  one  resulted  in  a  punishment  and  in  this  way  an 
attempt  was  made  to  have  the  association  formed  quickly. 
The  rye  bread  was  soaked  in  a  solution  of  quinine  bisulphate 
(about  I  per  cent,  although  no  attempt  was  made  to  keep 
the  bitterness  a  constant  factor).  The  white  bread  con¬ 
tained  no  quinine  and  was  presented  in  a  comparatively 
moist,  fresh  state,  but  much  dryer  than  the  rye  bread  that 
had  been  soaked  in  the  solution  of  quinine  immediately  before 
the  experiments.  By  taking  the  white  bread  and  avoiding 
the  rye  bread  the  animals  were  to  show  their  ability  to  dis¬ 
criminate  these  brightnesses.^  In  these  experiments  and  in 
later  ones  to  be  reported  it  was  assumed  that  monkeys  dis¬ 
liked  bitter  tastes;  this  assumption,  it  will  be  noted,  proved 
to  be  true. 

To  obviate  the  objection  that  the  smell  of  the  quinine  or 
the  rye  bread  might  enable  the  animal  to  differentiate  the 
white  from  the  rye  bread,  the  two  pieces  of  bread  were  placed 
in  varying  positions  on  the  board.  At  times  they  were  placed 
at  equal  distances  from  the  front  of  the  cage  and  within  an 
inch  of  each  other.  In  other  tests  one  was  placed  directly 
in  front  of  the  other,  and  in  other  tests  the  positions  were 
irregularly  varied,  one  being  nearer,  the  other  farther  from 
the  cage.  It  might  still  be  objected  that  the  rye  bread  which 
was  wet  from  having  been  soaked  in  the  solution  of  quinine 
would  give  them  a  clue.  That  this  objection  was  not  met  in 
the  conduct  of  the  experiments  must  be  admitted,  but  the 
formation  of  the  association,  i.e.,  the  positive  reaction  would 
give  evidence  of  sharp  visual  discrimination. 


1  In  addition  to  its  darker  appearance,  there  was  a  hue  difference  in  the  rye  bread. 
The  latter,  however,  is  the  less  prominent  factor. 


i6 


WILLIAM  SHEPHERD. 


Nine  animals  were  tested  by  this  method,  i,  2,  3,  4,  5,  6 
7,  8  and  9.  This  plan  of  tests  was  very  gratifying  in  its 
results.  It  showed,  apparently,  complete  discrimination 
of  the  two  pieces  of  bread.  The  rapidity  with  which  the 
habit  of  taking  only  the  white  bread  was  formed  was  striking. 
This  is  especially  noticeable  when  we  compare  the  records 
of  the  same  monkeys  in  this  and  in  the  preceding  brightness 
tests.  As  table  I  shows,  only  from  i  to  14  trials  were  required 
for  each  of  the  eight  monkeys  to  establish  the  association. 
This  is  excluding  the  work  of  monkey  9,  which  also  dis¬ 
criminated  the  white  and  rye  bread,  but  which,  being  in  the 
same  cage  with  monkey  8,  could  have  seen  the  latter  select 
the  white  and  reject  the  rye,  and  might  be  said  to  have  learned 
from  or  to  have  imitated  monkey  8. 

TABLE  I. 


Discrimination  of  white  and  rye  breads.  Twenty-five  experiments  on  each  animal. 


ANIMALS. 

Mistakes  in  Trials 

Total  Mistakes. 

First  Day. 

Second  Day. 

I 

I,  2a,  4b 

I2C 

4 

2 

1,2a,  40,5,6,8 

14^ 

7 

3 

I,  20,  3,  4b,  6b,  8b,  120 

13c 

8 

4 

I,  3a 

2 

5 

I,  20 

2 

6 

I,  20 

2 

7 

I,  2b,  30,  40 

4 

8 

I 

I 

9 

a  Took  rye  bread  after  having  taken  white,  smelled  or  tasted,  or  both,  and  dropped 
without  eating. 

b  Took  rye  bread  after  having  taken  white,  and  ate  both. 

c  First  trial  at  second  day;  took  rye  bread  but  dropped  it  immediately  without 
smelling  or  tasting. 

d  Second  trial  of  second  day;  without  smelling  or  tasting. 

It  is  of  some  interest  to  note  the  individual  reactions  to 
the  two  stimuli  that  were  presented.  At  the  first  trial  each 
animal  took  both  pieces  of  bread,  placed  them  in  the  mouth 
and  began  to  eat.  In  many  cases  the  bitterness  had  a  retard¬ 
ing  or  inhibiting  effect,  for  the  animal  would  take  the  rye 


F/5  UA  L  DISCRIMINA  TION. 


17 


bread  from  the  mouth,  look  at  it,  smell  it,  and  then  either 
reject  or  reinsert  it  in  the  mouth. 

Monkey  i,  in  addition  to  eating  the  rye  bread  on  the  first 
trial,  took  the  piece  of  rye  bread  in  the  second  trial,  smelled, 
tasted  and  dropped  it.  The  bitter  bread  was  not  taken  on 
the  third  trial,  but  on  the  fourth  the  animal  took  first  the  white 
which  it  ate,  then  the  rye,  which  it  also  ate.  The  rye  bread 
was  not  taken  on  the  next  seven  trials  on  that  day.  On  the 
twelfth  test  (the  first  test  on  the  second  day)  the  animal  first 
took  the  white  bread  and  ate  it,  then  took  the  rye  bread  and, 
without  smelling  or  tasting,  dropped  it  immediately.  On 
this  and  on  the  following  days  all  other  tests  were  perfect  in 
that  only  the  white  bread  was  taken  and  the  rye  bread  not 
even  handled,  although,  as  has  previously  been  noted,  at 
times  the  rye  bread  was  placed  closer  to  the  cage  than  the 
white  bread. 

Similar  results  were  obtained  with  animals  2  and  3  as  is 
indicated  in  the  table.  The  rapidity  of  learning  is  remark¬ 
able  in  all  animals,  but  particularly  so  in  4,  5,  6,  8  and  9. 
In  each  of  these  animals  two  tests  were  sufficient  to  inhibit 
altogether  the  tendency  to  take  the  darker  bread.  This  find¬ 
ing  is  so  at  variance  with  the  results  of  comparable  tests  on 
other  animals  that  there  would  be  ample  opportunity  to  use 
the  results  as  an  indication  in  monkeys  of  some  form  of 
reasoningor  of  a  marked  activity  to  form  practical  judgments. 

Color  discrimination — white  and  red.  The  same 
general  plan  was  followed  as  in  the  white  and  rye  bread  tests. 
Rice,  cooked  to  such  a  consistency  as  to  be  stiff,  was,  however, 
used  instead  of  bread.  It  was  cut  into  small  pieces  of  approxi¬ 
mately  the  same  size.  Some  of  these  pieces  were  used  for  the 
white  stimulus,  and  others  when  colored  with  Congo  red  for 
the  red.  The  red  pieces  were  soaked  in  a  quinine  solution 
and  used  while  wet.  The  white  contained  no  quinine  and 
was  in  a  comparatively  dry  state.  The  precautions  noted  in 
the  previous  test  were  taken  to  prevent  an  animal  obtaining 
a  clue  from  either  the  relative  positions  or  the  smell  of  the 
pieces  of  food. 

The  nine  monkeys  which  had  been  used  in  the  white  and 


i8 


WILLIAM  SHEPHERD. 


rye  bread  experiments  were  tested  in  this  experiment.  The 
rapid  learning  to  take  the  white  rice  and  to  reject  the  red  rice, 
as  in  the  white  and  rye  bread  test,  was  notable.  From  i  to 
3  trials  were  sufficient  for  the  different  animals  to  form  the 
association.  Animal  i  took  the  red  rice  only  the  first  trial, 
and  a  similar  result  was  obtained  with  monkeys  2,  4,  5,  6, 
7,  8  and  9.  Monkey  3  took  the  red  rice  only  three  times,  on 
the  first,  second  and  fifth  trials.  Not  only  is  the  rapidity 
of  the  formation  as  striking  here  as  in  the  case  of  the  white 
and  rye  bread,  but  the  fact  that  all  but  one  of  the  animals 
formed  the  association,  or,  rather,  inhibited  the  tendency  to 
take  the  red  rice,  after  having  experienced  its  effect  only  once, 
may  be  taken  as  an  indication  of  some  form  of  reasoning. 

Color  discrimination — pink  and  green.  A  plan  was 
followed  in  the  next  test  similar  to  that  employed  in  the 
white  and  red  experiment.  A  smaller  amount  of  coloring 
matter  was  used  and  some  of  the  rice  was  colored  a  light  pink. 
The  pink  rice  also  contained  quinine.  Another  portion  of 
rice  was  colored  green,  and  this  portion  contained  no  quinine. 
The  pink  coloring  was  obtained,  as  has  been  said,  by  using 
a  weak  solution  of  Congo  red,  the  green  was  made  by  using 
a  solution  of  Malachite  green.  Both  kinds  of  rice  were  used 
while  wet,  and  in  this  experiment,  it  is  not  probable  that 
discrimination  could  take  place  on  account  of  difference  in 
the  light  reflecting  qualities  of  the  two  kinds  of  rice.  Care 
was  taken  to  have  the  two  colors  as  nearly  as  possible  of  the 
same  approximate  brightness.  To  this  end  the  two  colors 
were  mixed  and  compared  to  the  colors  pink  and  green  of  the 
same  approximate  brightnesss  on  a  color  scale  and  the  mixed 
colors  as  well  as  those  of  the  color  scale  were  also  tested  by 
the  minimal  perception  method  in  a  dark  room  to  insure 
their  being  of  approximately  the  same  relative  brightness 
{i.e.,  to  the  human  eye). 

In  mixing  the  rice  the  coloring  materials  were  not  meas¬ 
ured,  nor  was  the  relative  amount  in  proportion  to  the  water 
of  the  solutions  kept  constant,  nor  the  relative  proportions 
of  the  two  colors  to  each  other,  nor  to  the  amount  of  rice. 
The  color  solutions  were  usually  made  up  anew  each  day 


VISUAL  DISCRIMINATION. 


19 


and  there  was  inevitably  a  greater  or  less  variation  in  satura¬ 
tion  and  in  brightness  of  the  colors  in  different  tests.  These 
remarks  hold  true  in  all  the  color  tests.  While  criticism 
may  be  made  on  any  apparent  discrimination  on  the  basis 
of  hue  under  such  conditions,  to  the  writer  discrimination 
of  color  would  be  indicated  by  proper  reaction  from  the  very 
fact  of  the  variation  of  intensities.  This  will  be  pointed 
out  again  in  the  discussion  of  the  color  experiments.  As  in 
the  preceding  tests  the  same  control  precautions  were  taken 
to  prevent  the  animals  from  taking  a  cue  either  from  the 
position  or  from  the  smell  of  the  rice. 

In  this  test  the  monkeys  formed  the  habit  of  taking  the 
green  and  rejecting  the  pink  with  even  greater  rapidity  than 
in  the  white-red  test.  Table  II  gives  the  records  of  nine 
animals  which  were  tested. 

Color  discrimination — pink  and  yellow.  In  this  test 
the  same  plan  was  followed  as  in  the  preceding  experiments. 
The  pieces  of  pink  rice  contained  quinine,  while  the  yellow 
contained  no  quinine.  As  in  the  preceding  tests,  both  the 
pink  pieces  and  the  yellow  pieces  were  used  while  wet.  The 
pink  coloring  was  produced  by  the  same  means  as  in  the  last 
mentioned  experiment,  while  the  coloring  of  the  yellow  pieces 
of  rice  was  produced  by  the  addition  of  lead  chromate.  The 
test  was  controlled  by  the  same  means  as  in  the  pink-green 
experiment  to  secure  the  same  approximate  degree  of  bright¬ 
ness  in  the  colors  pink  and  yellow,  and  to  prevent  the  animal 
from  receiving  any  cue  from  either  the  smell  of  the  two 
pieces  of  rice,  or  from  their  relative  positions  or  relative  dis¬ 
tances.  The  same  animals  were  used  as  in  the  preceding 
tests,  monkeys  i,  2,  3,  4,  5,  6,  7,  8  and  9. 


1  The  colors  were  mixed  and  compared  to  the  colors  pink,  yellow,  green  of  the  same 
approximate  brightness  on  a  color  scale,  and  the  mixed  colors  on  the  color  scale  tested 
in  a  dark  room  for  quality  of  brightness.  In  the  different  experiments,  the  pieces  of 
rice  were  also  placed  at  varying  distances  from  the  animal  to  prevent  his  taking  a  cue 
either  from  the  smell  or  the  positions  of  the  two  pieces. 


20 


WILLIAM  SHEPHERD. 


The  following  is  the  record  for  the  animals  for  25  trials  each : 


No. 


1  took  yellow  in  each  trial;  took  pink  trial  i 

2  9 


3 

4 

5 

6 

7 

8 

9 


none 

none 

I 

none 

none 

none 

none 


Color  discrimination — pink,  yellow  and  green.  The 
same  method  was  employed  in  this  experiment  as  in  the 
preceding  ones.  In  this  case  the  three  colored  pieces  of 
rice  were  simultaneously  exposed.  The  pink  and  yellow 
contained  quinine,  the  green  contained  no  quinine.  The 


TABLE  II. 


Discrimination  of  pink  and  green  rice.  Twenty  experiments  on  each  animal. 


MONKEYS. 

MISTAKES  IN  TRIALS. 

TOTAL  MISTAKES. 

I 

3 

I 

2 

3 

I 

3 

I 

I 

4 

0 

0 

5 

0 

0 

6 

0 

0 

7 

L  2,  3,  4,  5,  6,  7, 

14 

8,  9,  10,  II,  12, 

13,  14,  15,  16, 

8 

0 

0 

■coloring  for  the  pink,  yellow  and  green  was  the  same  as  used 
in  the  preceding  tests,  each  was  used  while  wet.  Exactly 
the  same  means  to  control  the  tests  were  employed  as  above. 
The  same  monkeys  were  tested  as  in  the  white  and  rye  bread 
test,  the  white-red,  the  pink-green,  and  the  pink-yellow  experi¬ 
ments.  Here  again  the  rapidity  of  the  rise  of  the  habit  of  , 
response  is  striking.  Table  III  gives  the  record  of  each 
monkey  for  25  trials. 


VISUAL  DISCRIMINATION. 


21 


TABLE  III. 


Discrimination  of  pink,  yellow  and  green  rice.  Twenty-jive  experiments  each  animal. 
Ten  experiments  first  day,  fifteen  on  second  day.  y,  took  yellow;  p,  took  pink. 


MONKEYS. 

MISTAKES  IN  TRIALS. 

TOTAL  MISTAKES. 

I 

I  y, 

I 

2 

I  y, 

I 

3 

I  y, iiy 

2 

4 

I  y 

I 

5 

I  y,  2  y,  3  y,  4  y,  ii  yp,  12  y 

6 

6 

I  y,  2  y,  3  y,  4  y,  5  y,  6  y. 

10 

II  y,  12  y,  13  y,  14  y. 

7 

I  y,  2  y,  3  y,  4  y,  s  y,  6  y,  7  y, 

16 

8  y,  9  y,  10  y,  n  y,  12  y, 

13  y,  16  y,  17  y,  i8  y, 

8 

I  y,  2  y,  3  y,  4  y,  5  y,  6  y, 

10 

7y  II  y,  12  y,  13  y, 

We  see  from  the  records  and  tables  that  the  nine  animals 
quickly  learned  to  select  the  rice  that  contained  no  quinine 
and  to  leave  the  quinine  rice  alone.  The  learning  to  respond 
quickly  was  much  more  rapid  than,  so  far  as  I  am  aware, 
that  of  any  other  monkeys  which  have  been  studied  for 
visual  discrimination.  In  many  cases,  one  trial  was  sufficient 
to  inhibit  any  tendency  to  take  the  quinine  rice,  and  the 
rapidity  in  inhibition  of  the  wrong  response  was  undoubtedly 
due  to  the  use  of  a  punishment  or  to  the  association  of  a 
disagreeable  sensation,  i.e.,  to  the  quinine  in  the  rice. 

Another  factor  in  the  rapid  formation  of  the  habit  of 
avoiding  the  quinine  rice,  in  the  case  of  pink  in  the  pink- 
green  rest,  was  probably  the  knowledge  or  memory  of  dis¬ 
agreeableness  in  red  rice  in  the  white-red  test  immediately 
preceding.  In  the  pink-yellow  test  and  in  the  pink-yellow- 
green  test,  knowledge  of  quinine  in  pink  in  the  preceding 
tests,  was  also  probably  a  factor  in  their  rapid  discrimina¬ 
tion.  In  the  pink-yellow-green  test  the  experience  of  the 
preceding  tests  of  pink-bitter,  yellow-good,  green-good  helps 
to  explain  the  number  of  mistakes  in  yellow  rice.  But,  with 
all  these  allowances,  we  still  have  evidence  of  rapid  formation 
of  the  habits  of  selecting  one  color  and  of  rejecting  another, 
and  thereby  apparently  discriminating  the  colors  red,  pink, 


22 


WILLIAM  SHEPHERD. 


yellow  and  green.  That  discrimination  has  taken  place 
cannot  be  doubted,  but  the  question  arises:  did  the  animals 
discriminate  the  colors  as  hues,  or  as  merely  brightness 
values? 

Watson  (2),  in  very  carefully  controlled  tests  made  on 
three  monkeys  in  1908,  failed  to  find  evidence  satisfactory 
to  him  that  his  animals  discriminated  colors  as  hues.  From 
later  tests  (3)  also,  on  monkeys,  he  is  still  not  prepared  to 
affirm  whether  such  discrimination  is  of  color  or  of  mere 
brightness.  Yerkes  (4),  from  the  results  of  his  well-controlled 
experiments  on  the  dancing-mouse,  takes  a  view  of  the  matter 
similar  to  that  of  Watson.  Both  condemn  the  use  of  cards, 
filters,  etc.,  in  experimenting  on  color  discrimination.  They 
believe  such  methods  are  too  loose  to  have  much  value 
and  they  urge  the  use  of  more  exact  methods  of  determining 
the  matter. 

In  the  experiments  on  color  discrimination  reported  in 
this  paper,  as  has  already  been  stated,  the  criticism  that  the 
method  used  is  a  loose  one  may  be  urged.  The  exact  propor¬ 
tion  of  the  different  coloring  materials  to  the  bread  or  rice 
and  to  the  amount  of  water  in  making  the  solutions  was  not 
determined.  Furthermore,  it  may  be  said  that  as  the  color¬ 
ing  solutions  were  mixed  anew  almost  daily,  it  would  hardly 
be  possible  not  to  have  some  variation  in  the  intensities  of 
the  colors  at  different  times.  This  is  true,  notwithstanding 
that  means  were  taken  to  control  the  experiments,  viz.,  com¬ 
parison  with  certain  color  standards.  Shall  we  infer  that  the 
experiments  were  thereby  so  vitiated  as  to  have  little  or  no 
value  as  a  test  of  color  discrimination?  Such  will  doubtless 
be  the  view  of  some,  at  least  on  first  thought,  but,  to  the 
writer,  these  inaccuracies  in  method  point  to  a  different 
conclusion. 

It  is  admitted  that  the  method  and  apparatus  used  in  the 
experiments  herein  reported  appear  loose  and  crude  when 
compared  to  the  ingenious  methods  and  complicated  appara¬ 
tus  used  in  the  experiments  of  Watson  and  others.  It  may 
also  be  urged  that  my  experiments  take  no  adequate  account 
of  the  question  of  ‘monochromatic  bands’  in  the  problem 


VISUAL  DISCRIMINATION. 


23 


of  color  vision.  To  this  we  may  reply  that  in  the  very  loose¬ 
ness  and  naturalness  of  the  tests  is  to  be  found  perhaps  the 
strongest  evidence  of  the  discrimination  of  color  by  the 
animals  which  I  tested.  On  the  other  hand  I  would  point  to 
the  highly  artificial  character  of  the  methods  used  by  some 
experimenters.  The  complication  of  apparatus  with  its 
reflectors,  electric  shocks  and  other  appendages  is  artificial 
in  the  extreme  and  and  must  result  in  an  artificial  attitude  on 
the  part  of  the  animal.  The  tests,  with  complicated  appara¬ 
tus,  conducted  in  a  dark  room,  bring  about  another  artificial 
and  unusual  situation,  viz.,  the  necessity  for  dark  adaptation 
by  the  animal.  The  method  employed  in  these  experiments 
leaves  to  the  animal  a  large  amount  of  freedom  and  places 
the  animal  in  a  position  as  natural  as  is  possible  in  such  work. 
If,  as  has  been  urged  by  some,  the  experiments  with  colored 
cards  and  filters  may  only  mean  that  the  animals  react  to 
brightness  or  intensity,  and  not  to  hue  relations,  we  should 
expect  an  animal  to  react  to  a  definite  relation  of  brightness 
unless  we  admit  in  animals  some  complex  form  of  the  feel¬ 
ing  of  relation  or  a  certain  amount  of  inferential  reasoning. 
Such  an  explanation  {i.e.,  brightness  discrimination)  may  be 
justified  when  the  red-white  test  be  considered  alone.  But 
how  may  we  explain  the  results  in  the  pink-green  test?  Half 
of  the  animals  used  in  the  latter  test  made  no  mistakes. 
From  the  beginning  of  this  experiment  pink  rice  was  avoided, 
although  it  is  not  possible  that  the  animals  had  any  experi¬ 
ence  with  red  or  pink  rice  previous  to  the  time  of  these 
experiments.  Four  of  the  animals,  therefore,  reacted  prop¬ 
erly  to  a  hue  of  an  intensity  or  brightness,  considered 
from  the  human  standpoint,  very  different  from  that  to  which 
the  animals  had  learned  to  react.  Do  not  these  positive 
reactions  indicate  rather  clearly  that  somehow  or  in  some  way 
the  pink  rice  has  been  taken  to  be  equivalent  to  or  mean  some 
thing  similar  to  red  rice?  Do  not  these  results  rather  lead 
to  the  conclusion  that  it  is  not  a  difference  in  brightness  or 
in  intensity  which  has  led  to  the  appropriate  adjustment, 
but  rather  a  difference  in  hue?  Furthermore,  the  fact  that 
in  the  pink-green  test  the  animals  took  the  green  and  avoided 


24 


WILLIAM  SHEPHERD. 


the  pink  regardless  of  the  difference  in  the  amount  of  color 
is  evidence  that  color  as  such  was  an  important,  and  probably 
the  only,  factor  in  the  discrimination.  This  view  receives 
added  weight  from  the  similar  results  under  similar  condi¬ 
tions  (of  approximate  brightness  and  color)  in  the  pink- 
green-yellow  tests. 

It  may,  however,  be  urged  that  the  carrying  over  of  a 
habit  from  a  red  to  a  pink  indicates  merely  a  dullness  in  dis¬ 
crimination,  that  the  red  and  pink  may  have  been  sensed  or 
perceived  as  approximate  equivalents.  It  must  be  admitted 
that  this  may  be  so,  but  the  wide  differences  in  the  intensity 
of  the  red  and  pink  would  indicate  rather  clearly  that  the 
discrimination  (or,  comparison,  if  you  will)  has  been  due  not 
to  simple  intensity  relations  but  to  hue  or  color  similarities. 
For  the  discussion  of  the  results  in  the  pink-green  tests,  we 
may  make  two  assumptions,  that  the  two  kinds  of  rice  were 
of  equal  or  unequal  brightness.  If  we  assume  an  equal 
brightness,  the  experiments  must,  it  seems  to  me,  be  con¬ 
sidered  to  show  that  discrimination  has  taken  place  because 
of  difference  in  hue.  If  we  assume  the  two  kinds  of  colored 
rice  to  have  been  of  unequal  brightnesses,  we  must,  remember¬ 
ing  the  variations  in  the  experiments  on  different  days,  con¬ 
sider  that  the  discrimination  has  taken  place  in  spite  of  this 
variation.  The  results  then  lead  to  the  conclusion  that  the 
discrimination  has  been  due  to  a  factor  different  to  that  of 
intensity  on  the  physical  side,  or  that  of  brightness  on  the 
mental.  The  only  other  factor  which,  in  man,  would  pro¬ 
duce  such  a  reaction,  is  that  of  color. 

A  comparison  of  the  results  obtained  in  the  different  color 
tests  strengthens  this  view.  The  consideration  of  the  results 
in  the  white-red,  pink-green  and  pink-yellow  tests  is  instruc¬ 
tive.  Monkeys  4,  5  and  8  which  had  one  experience  in  tast¬ 
ing  bitter  red  rice  did  not  take  the  pink  rice  in  the  succeed¬ 
ing  tests.  Now,  it  must  be  remembered  that  these  monkeys 
had  no  previous  experience  with  pink  rice,  and  their  avoid¬ 
ance  of  it  can  be  accounted  for  only  on  the  assumption  that 
something  in  the  pink  rice  gave  a  clue  to  the  animal. 

The  differences  (to  us  humans,  of  course)  between  the  red 


VISUAL  DISCRIMINATION 


25 


and  the  white  rice  are  three-fold:  color,  intensity,  and,  akin 
to  the  latter,  reflecting  quality  or  sheen.  The  last  named 
was  due  to  the  differences  in  moisture,  the  red  rice  having 
been  soaked  in  the  quinine  solution  only  a  few  minutes  before 
the  tests  were  begun.  The  sheen  of  the  pink,  green  and  yel¬ 
low  rice  was  the  same,  for  all  were  equally  moist  at  the  time 
of  the  experiments.  There  were,  therefore,  only  two  possible 
differences  between  these  colors,  viz.,  hue  and  intensity. 

If  the  avoidance  of  pink  is  to  be  explained,  we  must  admit 
that  it  was  due  either  to  hue  or  to  intensity.  If  it  were  due 
to  a  feeling  of  intensity  difference,  to  an  inference  (taking  the 
human  standpoint,  of  course)  that  darkness  means  bitter 
and  lightness  means  sweet  we  must  account  for  a  transfer 
from  the  red  (very  dark)  to  the  pink  (slightly  dark).  We 
must  also  account  for  the  transfer  in  connection  with  the 
other  stimuli  (green)  which  from  tests  was  found  to  have  an 
approximate  intensity  equal  to  that  of  pink.  So  far  as  I 
can  see  at  present,  the  only  possible  intensity  explanation 
of  this  transfer  is  that  red  has  a  low  brightness  effect  in  com¬ 
parison  with  other  colors.  However,  we  know  that  the  inten¬ 
sities  of  the  red  and  the  pink  rice  varied  greatly  from  each 
other,  and  we  are  forced  to  account  for  the  phenomenon  of 
transfer  on  the  basis  of  some  quality  not  so  markedly  changed. 
This,  I  believe,  is  the  hue. 

To  sum  up  we  may  say  that  the  evidence  is  in  favor  of  the 
conclusion  that  monkeys  have  the  ability  to  discriminate 
colors  as  such.  So  far  as  is  known  of  the  structure  of  the 
retina  and  of  the  remainder  of  the  visual  apparatus  there  is 
nothing  to  indicate  any  difference  to  the  human  mechanism, 
and,  from  this  point  of  view,  no  reason  exists  why  the  monkey 
family  may  not  be  able  to  differentiate  the  four  colors  red, 
green,  yellow  and  blue.  The  rapidity  of  formation  of  the 
association  between  the  light  bread  and  agreeableness  and 
that  between  the  dark  bread  (rye)  and  disagreeableness,  as 
evidenced  by  their  selection  of  the  former  and  their  avoidance 
of  the  latter,  is  indicative  of  sharp  visual  (brightness  or 
intensity)  discrimination.  The  selection  of  one  color  and 
the  rejection  of  another  in  spite  of  differences  in  intensities 


26 


WILLIAM  SHEPHERD. 


speaks  strongly  for  the  discrimination  of  hue.  The  transfer 
of  the  habit  from  red  to  pink  is  indicative  that  the  animals 
had  some  form  of  feeling  of  relation  or  of  similarity  between 
the  colors  as  such,  or  that  the  hue  (in  itself  and  independent 
of  intensity)  acted  as  the  appropriate  stimulus  to  inhibit  the 
tendency  to  take  the  particular  food. 

Auditory  Discrimination — Noise.  The  apparatus  used  was 
a  wooden  box  22  x  i8  x  lo  inches  and  a  small  board  or  slat 
18  X  3^  X  I  inches  arranged  to  strike  the  box  and  thus  make  a 
noise.  One  end  of  the  board  or  slat  was  fastened  to  the  top 
of  the  box  by  a  leather  hinge.  By  raising  the  free  end  of  the 
slat  and  suddenly  letting  it  go,  it  struck  the  top  of  the  box 
and  made  a  sound  varying  in  loudness  with  the  force  with 
which  it  struck.  To  give  two  sounds  of  different  degrees 
of  intensity  or  loudness  two  small  sticks,  one  3  inches  in 
length,  the  other  5  inches  in  length,  were  separately  used  to 
be  placed  perpendicular  to  the  box  and  under  the  free  end 
of  the  board.  By  pressing  slightly  on  the  slat  near  the  hinge, 
and  suddenly  removing  the  shorter  stick,  the  board  would 
strike  the  box  and  produce  a  noise  of  a  noticeable  intensity, 
and  by  pressing  on  the  board  as  before,  and  withdrawing  the 
larger  stick  that  had  been  placed  at  the  free  end,  the  board 
would  strike  the  box  and  produce  a  much  louder  noise.  The 
same  pressure,  as  nearly  as  possible,  was  exerted  by  the 
experimenter  on  the  board  in  both  cases.  By  going  upon 
a  platform  arranged  inside  the  cage  when  the  louder  noise 
was  made,  the  animals  were  to  show  their  discrimination  of 
the  louder  and  lesser  noises.  They  were  fed  on  the  platform 
when  the  louder  noise  was  made,  and  were  not  fed  when  the 
lesser  noise  was  made.  The  noise  apparatus  was  manipu¬ 
lated  near  the  closed  side  of  the  cage  in  which  the  monkeys 
were  kept.  It  was  out  of  sight  and  it  was  not  possible  that 
the  reactions  were  made  to  stimuli  other  than  the  sounds. 
The  louder  and  lesser  noises  were  made  in  an  irregular  order. 
Three  animals,  4,  5  and  6,  were  tested  by  this  method. 

Monkey  4  formed  the  habit  of  responding  to  the  louder 
sound  and  not  to  the  lesser  in  eight  days  of  10  trials  each, 
i.e.,  10  trials  with  each  sound)  or  in  80  trials  in  all.  In  the 


A  UDITOR  Y  DISCRIMINA  TION. 


27 


first  day’s  trials  he  responded  to  the  louder  sound  once  in  the 
10  trials  given  him,  and  to  the  lesser  sound  twice  in  the  same 
number  of  trials.  In  10  trials  on  the  eighth  day  he  always 
responded  to  the  louder  noise  correctly  and  to  the  lesser 
noise  only  once  in  the  same  number  of  trials.  On  the  ninth 
day  he  made  no  errors  in  the  10  trials  given  him.  Monkey 
6  formed  the  association  in  eleven  days  of  10  trials  each. 
On  the  first  day  she  responded  to  the  louder  sound  three  times 
and  to  the  lesser  four  times.  On  the  eleventh  day  she  re¬ 
sponded  to  the  louder  sound  nine  times  and  to  the  lesser 
sound  once.  She  made  no  errors  in  the  10  trials  for  each 
sound  on  the  twelfth  day.  In  the  time  devoted  to  this  work 
with  number  5,  he  did  not  form  a  perfect  association.  In 
thirteen  days’  experiments  of  10  trials  each  he  finally  came 
to  respond  to  the  loud  sound  in  about  75  per  cent  of  the  trials. 
His  inhibition  of  response  to  the  lesser  sound  was  less  perfect, 
or  about  50  per  cent.  Had  the  tests  been  continued  it  seems 
likely  he  would  have  become  perfect  in  discriminating  the 
two  sounds.  It  is  of  some  interest  to  note  the  apparent 
inferior  ability  of  5  in  comparison  with  4  and  6  in  this  experi¬ 
ment.  The  work  of  5  appeared  typical  of  all  his  work  re¬ 
ported  in  this  paper.  Inhibition  was  apparently  his  weak 
point,  for  he  responded  to  no  matter  what  form  of  stimulus. 
The  difference  illustrates  the  individual  variations  in  mental 
capacity  of  the  different  animals. 

Sound  discrimination,  Pitch.  Kalischer  (5,  p.  204  ff.)  has 
reported  experiments  on  sound  discrimination  with  dogs, 
which  animals  show  an  ability  to  discrimination  pitch.  Al¬ 
though  interested  in  the  matter  more  from  a  physiological 
than  a  psychological  standpoint,  he  incidentally  obtained 
satisfactory  evidence  of  discrimination  of  pitch  by  his  animals. 
His  method  was  to  sound  a  certain  note  on  an  organ  or  har¬ 
monium  as  a  sign  that  the  animal  should  react  in  a  certain 
way,  such  as  snapping  at  a  piece  of  meat.  When  a  different 
note  was  sounded  the  dog  was  not  to  react  and  was  not  fed. 
Selionyi  using  a  form  of  the  Tawlow  method’  on  dogs  has 
also  lately  obtained  evidence  of  discrimination  by  them  of 
the  tones  of  an  organ,  organ  pipes  and  of  two  whistles.  He 


28 


WILLIAM  SHEPHERD. 


also  was  chiefly  interested  in  sound  discrimination  from  a 
physiological  standpoint. 

In  experiments  on  auditory  discrimination  in  raccoons 
made  by  the  present  writer  in  1906,  reported  by  Cole  (16, 
p.  230)  evidence  of  pitch  discrimination  by  those  animals 
was  obtained.  In  the  experiments  on  pitch  to  be  reported 
in  this  paper  I  used  the  same  plan  that  I  had  employed  with 
the  raccoons,  and  which  is  similar  to  the  method  Kalischer 
has  used.  An  ordinary  German  mouth  harp  or  harmonica 
A  was  used.  When  I  sounded  the  higher  note,  A  3,  the 
monkey  was  to  go  upon  the  platform  used  in  the  preceding 
noise  tests,  and  was  fed  there  when  the  note  was  sounded. 
When  the  lowest  note,  A  i  (two  octaves  lower),  was  sounded 
he  was  not  to  go  up  and  was  not  fed.  The  notes  were  sounded 
in  an  irregular  order  so  the  animal  might  not  react  in  a  rhythm 
to  the  sounds.  Care  was  taken  to  sound  the  notes  with  the 
same  degree  of  intensity,  as  nearly  as  possible.  I  took  the 
usual  precautions  that  the  animal  should  not  obtain  a  cue 
from  my  looks,  motions  or  in  any  other  manner,  and  react 
to  these  stimuli  rather  than  the  tones. 

The  records  for  the  different  animals  are  as  follows: 

Monkey  4  formed  the  habit  of  responding  to  the  high  note, 
A  3,  and  not  responding  to  the  low  note,  A  i,  in  three  days 
tests  of  10  trials  each.^  On  the  first  day  monkey  4  responded 
to  the  high  note  six  times  in  10  trials,  and  not  at  all  to  the 
low  note.  On  the  third  day  he  responded  to  the  high  note 
ten  times  and  to  the  low  note  three  times.  On  the  fourth 
day  of  the  experiment  (three  days  after  the  experiments  just 
noted)  he  responded  to  the  high  note  ten  times  in  10  trials 
and  to  the  low  note  not  at  all  in  the  same  number  of  trials. 
WTen  tested  on  the  fifth  day,  two  days  later,  he  was  perfect 
in  10  trials. 

Monkey  6  formed  the  association  in  four  days,  in  40  trials 
in  all.  On  the  first  day  she  responded  to  the  high  note  twice 
in  ten  trials  and  to  the  low  note  not  at  all.  On  the  fourth 
day  she  responded  to  the  high  note  nine  times  and  to  the 


1  i.e.,  ten  trials  of  the  high  note  and  ten  trials  of  the  low  note. 


INHIBITION  OF  HABIT. 


29 


low  note  once  in  10  trials  of  each  note.  In  the  10  trials  on 
the  fifth  day  she  was  perfect. 

Monkey  5  did  not  form  the  habit  of  correct  response  in 
six  days’  tests  of  10  trials  each.  In  the  10  trials  of  high  and 
low  pitch  on  the  sixth  day  he  responded  to  the  high  note  six 
times  and  to  the  low  note  only  once. 

If  we  may  generalize  from  the  work  of  the  animals  tested 
in  the  above  experiments  we  may  conclude  that  Rhesus 
monkeys  discriminate  quantitative  differences  in  noises.  They 
also  discriminate  musical  notes  of  widely  different  pitch. 
These  experiments  also  indicate  that  monkeys  learn  to  dis¬ 
criminate  pitch  with  considerably  more  facility  than  do 
raccoons  in  similar  tests. 

Inhibition  of  habit. 

The  activities  or  modes  of  behavior  of  animals,  including 
man,  are  of  five  kinds:  {a)  reflex  actions;  (6)  instinctive  actions; 
(c)  habitual  actions;  (d)  intelligent  actions; '(e)  rational 
actions.  These  different  actions,  in  varying  degrees,  charac¬ 
terize  the  different  orders  of  animals.  Generally  speaking, 
the  lower  the  order  of  the  animal  the  more  the  a  form  of 
action  is  present,  and  the  higher  the  order  of  the  animal  the 
more  the  d  and  e  forms  of  action  are  present.  The  lower 
forms  are,  however,  basal  for  man  as  well  as  for  the  amoeba. 

Habitual  actions  are  seen  not  only  in  the  behavior  of 
animals  of  the  higher  orders  but  also  in  the  activities  of  man. 
Many  apparently  intelligent  actions  of  man  are  of  the  nature 
of  habit.  To  say  that  habit  dominates  man’s  actions  to  a 
very  large  degree,  and  reason  to  a  very  small  degree  is  only 
to  state  the  simple  truth. 

Previous  observations  have  indicated  to  comparative  psy¬ 
chologists  that  monkeys  and  other  mammals  have  a  marked 
tendency  to  form  habits  of  action.  This  was  well  shown 
by  Lloyd  Morgan  and  many  others.  A  certain  perceived 
stimulus  is  followed  by  an  agreeable  or  by  a  disagreeable 
result,  and  an  animal  soon  forms  the  habit  of  reacting  in  the 
appropriate  manner  when  the  stimuli  are  given.  The  for- 


30 


WILLIAM  SHEPHERD. 


mation  of  habits  is,  however,  only  one  way  of  meeting  the 
conditions  of  the  environment.  Habits  once  acquired  often 
become  useless,  and  sometimes  have  to  be  replaced  by  actions 
opposite  in  character.  In  other  words  the  inhibition  or  the 
replacement  of  a  habit  is  often  necessary  to  the  well  being 
of  an  animal  or  of  man,  and  the  ability  to  inhibit  definite 
modes  of  reaction,  including  reflex  tendencies,  is  important 
for  advancement. 

To  test  in  some  measure  the  ability  of  monkeys  to  inhibit 
a  recently  formed  habit  four  experiments  were  made.  Three 
monkeys  which  had  learned  to  discriminate  white  (normal) 
from  rye  (quinine)  bread  were  reviewed  on  this  work  daily 
for  seven  days  in  order  that  the  habit  be  firmly  established. 
A  rest  period  of  seven  days  was  given,  and  then  the  memory 
tested.  The  results  of  the  latter  test  showed  a  perfect  reten¬ 
tion  by  all  the  animals.  On  the  succeeding  day  each  monkey 
was  presented  with  some  pieces  of  rye  bread  that  had  not 
been  soaked  in  quinine.  Then  an  experiment  was  performed 
in  which  the  rye  bread  was  not  made  bitter.  These  tests 
were  continued  for  seven  days,  lo  tests  on  each  day.  The 
results  are  given  in  Table  IV.  It  will  be  noticed  that  on  the 
first  day  monkeys  6  and  8  disregarded  the  rye  bread,  and 
monkey  8  continued  to  disregard  it  for  two  more  days. 
Monkey  7  on  the  fourth  trial  on  the  first  day  took  the  white 
bread  first  and  then  the  rye.  Five  times  thereafter  she  repeated 
this,  and  the  habit  of  refusing  the  rye  bread  when  it  was 
simultaneously  exposed  with  the  white  was  broken.  There¬ 
after,  on  the  six  succeeding  days  of  the  experiment  she  left 
the  rye  bread  only  once. 

After  this  series  a  second  test  was  made  in  which  the 
white  bread  was  made  bitter  with  quinine.  Both  pieces  of 
bread  were  presented  simultaneously  on  a  board,  as  in  the 
previous  experiments.  The  results  of  the  tests,  10  experi¬ 
ments  a  day  for  seven  days,  are  given  in  Table  V.  It  will 
be  seen  that  the  animals  .soon  learned  to  avoid  the  bitter 
bread.  The  mistake  made  by  monkey  6  on  the  second  day 
was  only  a  partial  mistake  for  the  animal  picked  up  the  white 
bread,  smelled  it  and  immediately  dropped  it.  The  inhibi- 


INHIBITION  OF  HABIT. 


31 


tion  in  the  case  of  monkey  7  was  fixed  on  the  first  day  after 
four  mistakes  had  been  made, 

A  third  series  was  then  made  in  which  the  small  pieces  of 
bread  (white,  bitter;  rye,  normal)  were  presented  successively. 
In  these  experiments  the  animal  had  a  choice  of  taking  or 
of  leaving  the  single  piece,  white  or  rye.  The  results  are 
given  in  Table  VI.  It  will  be  seen  that  the  three  animals 
avoided  the  white  bread  on  the  first  day  of  the  experiments, 
but  that  on  the  second  all  took  the  white  at  least  once.  On 
the  second  day  monkey  6  took  the  white  bread  six  times, 
and  monkey  8  four  times.  After  these  experiments  both  ani¬ 
mals  disregarded  the  white  bread  when  it  was  presented  to 
them  on  the  board,  even  though  they  were  very  hungry.  Only 
once  during  the  remainder  of  these  tests  did  monkey  6  touch 
the  white  bread.  On  the  fourth  day,  when  the  white  bread 
was  presented,  she  put  her  hand  through  the  wire  of  the  cage 
and  swept  the  piece  off  the  board. 

The  fourth  series  of  experiments  was  begun  after  the 
seven  days  of  series  3.  In  this  last  series  the-  breads  were 
presented  to  the  animal  by  the  experimenter,  to  see  if  the 
inhibition  effect,  or  the  new  habit  of  leaving  the  white  bread 
was  associated  with  the  presentation  of  the  bread  upon  the 
board  outside  the  cage.  Each  piece  of  bread  was  taken  by 
the  experimenter  in  his  fingers  and  held  just  within  the  wire 
netting  of  the  cage.  Even  with  this  added  inducement 
monkey  6  refused  to  take  the  white  bread,  but  both  of  the 
other  animals  finally,  and  monkey  7  repeatedly,  took  it. 
In  the  70  trials  with  monkey  7,  she  took  the  white  bread 
fourteen  times.  At  the  sixth  trial  on  the  fifth  day  monkey 
7  struck  at  me  when  I  offered  her  the  white  bread,  as  if  angry 
that  it  should  be  presented  to  her.  Monkey  8  took  the  white 
bread  twice  on  the  second  day,  but  after  he  had  smelled  it  he 
dropped  it.  On  the  fifth  day  he  once  reached  toward  the 
white  bread  that  was  offered  him,  but  drew  back  before  he 
had  touched  it.  On  the  sixth  day  he  struck  at  the  white 
bread  or  at  me  just  as  he  had  monkey  7  on  the  previous  day. 

These  experiments  show,  on  the  part  of  the  monkeys 
investigated,  a  rapid  inhibition  of  a  previously  formed  habit. 


32 


WILLIAM  SHEPHERD. 


and  a  rapid  acquisition  of  a  habit  opposed  to  the  original 
habit.  The  acquisition  of  the  new  habit,  however,  took  a 
much  longer  time  than  that  of  the  original  habit,  as  can  be 
seen  from  a  comparison  of  the  results.  In  the  later  experi¬ 
ments  so  many  new  factors,  especially  those  of  tempting  the 
animal  by  single  presentations,  were  introduced  that  the 
curves  of  learning  cannot  be  directly  compared.  It  would 
be  fair,  however,  to  compare  the  results  in  Table  V  with  those 
in  Table  I.  When  this  is  done  it  is  seen  that  the  replacement 
of  the  association  is  almost,  if  not  equally,  as  rapid  as  the 
formation.  Should  this  result  be  true  for  other  activities 
of  the  monkey,  it  would  indicate  a  rather  high  degree  of 
adaptivity,  which  goes  far  towards  the  production  of  appar¬ 
ently  intelligent  actions. 


TABLE  IV. 


Inhibition  of  habits.  All  monkeys  had  learned  to  avoid  quinine  {rye)  bread;  no  quinine 
in  either  bread  for  this  test.  W  =  took  white,  R  =  took  rye.  T  en  trials  each  animal 
daily. 


MONKEYS  AND 
SERIAL  DAYS. 

I 

2 

3 

4 

s 

6 

7 

6 

W 

lO 

w 

8 

w 

lO 

W 

lO 

w 

lO 

W 

lO 

W 

10 

R 

o 

R 

8 

R 

lO 

R 

lO 

R 

lO 

R 

lO 

R 

lO 

7 

W 

lO 

W 

lO 

W 

lO 

W 

lO 

W 

lO 

W 

lO 

W 

lO 

R 

5 

R 

lO 

R 

lO 

R 

9 

R 

10 

R 

lO 

R 

lO 

8 

W 

lO 

W 

lO 

W 

lO 

W 

lO 

W 

lO 

W 

lO 

W 

lO 

R 

o 

R 

o 

R 

o 

R 

4 

R 

8 

R 

lO 

R 

lO 

TABLE  V. 


Inhibition  of  habits.  All  monkeys  had  been  practised  on  preceding  tests  {Table  IV). 
Quinine  in  white  bread,  rye  bread  in  natural  stale.  Simultaneous  presentation.  R 
took  rye,  W  =  took  white  bread.  Ten  trials  daily. 


MONKEYS  AND 
SERIAL  DAYS. 

I 

2 

3 

4 

s 

6 

7 

W 

I 

W 

I* 

w 

I 

W 

I 

W 

lO* 

W 

lO 

W 

lO 

6 

R 

lO 

R 

lO* 

R 

lO 

R 

lO 

R 

lO* 

R 

lO 

R 

lO 

W 

4 

W 

o 

W 

o 

W 

o 

W 

o 

W 

o 

W 

o 

7 

R 

lO 

R 

lO 

R 

lO 

R 

lO 

R 

lO 

R 

lO 

R 

lO 

W 

3 

W 

I 

W 

o 

W 

o 

W 

o 

W 

o 

W 

o 

8 

R 

lO 

R 

lO 

R 

lO 

R 

lO 

R 

lO 

R 

lO 

R 

lO 

IMITATION. 


33 


TABLE  VI. 


Inhibition  of  Habits.  All  animals  had  been  previously  practised  on  experiments  recorded 
in  Tables  IV  and  V.  Quinine  in  white  bread,  rye  bread  in  natural  state.  Succes¬ 
sive  presentations.  W  =  took  white,  R  =  rook  rye  bread.  Ten  times  daily. 


MONKEYS  AND 
SERIAL  DAYS. 

I 

2 

3 

4 

s 

6 

7 

W 

I 

W 

6 

w 

0 

W 

0 

W 

0 

w 

0 

W 

0 

6 

R 

10 

R 

10 

R 

10 

R 

10 

R 

10 

R 

10 

R 

10 

W 

0 

W 

I 

W 

I 

W 

S 

W 

I 

W 

I 

W 

2 

7 

R 

10 

R 

10 

R 

10 

R 

10 

R 

10 

R 

10 

R 

10 

W 

0 

W 

4 

W 

0 

W 

0 

W 

0 

W 

0 

W 

0 

8 

R 

10 

R 

10 

R 

10 

R 

10 

R 

10 

R 

10 

R 

10 

TABLE  VII. 

Inhibition  of  Habits.  All  animals  had  been  previously  practised  on  experiments  recorded 
in  Tables  IV,  V,  and  VI.  Quinine  in  white  bread,  rye  bread  in  natural  state.  Suc¬ 
cessive  presentations  through  wire  netting  of  cage  instead  of  outside.  W  =  took  white, 
R  =  took  rye  bread.  Ten  trials  daily. 


MONKEYS  AND 

SERIAL  DAYS. 

I 

2 

3 

4 

s 

6 

7 

W 

0 

W 

0 

W 

0 

W 

0 

W 

0 

w 

0 

w 

0 

6 

R 

10 

R 

10 

R 

10 

R 

10 

R 

10 

R 

10 

R 

10 

W 

0 

W 

0 

W 

3 

W 

5 

W 

2 

W 

3 

W 

4 

7 

R 

10 

R 

10 

R 

10 

R 

10 

R 

10 

R 

10 

R 

10 

W 

0 

W 

2 

W 

I 

W 

0 

W 

I 

W 

0 

W 

0 

8 

R 

10 

R 

10 

R 

10 

R 

10 

R 

10 

R 

10 

R 

10 

Imitation. 

Whether  or  not  the  higher  animals  learn  by  imitation  is  a 
mooted  question  among  comparative  psychologists.  Involv¬ 
ing  as  it  does  the  presence  of  ideation  or  of  ‘transferred 
association’  in  the  animal  mind,  it  is  of  the  utmost  impor¬ 
tance  that  this  mental  function  be  carefully  considered. 
Most  experiments  in  the  field  of  comparative  psychology  are 
inclined  to  deny  the  higher  forms  of  imitation  to  animals. 
Morgan  (7),  Thorndike  (8,  9)  Yerkes  (4),  and  Watson  (10), 
take  this  ground,  while  Kinnaman  (ii),  Hobhouse  (12), 
Berry  (13),  Haggerty  (14)  and  others  believe  they  have 
found  evidence  of  imitation,  apart  from  mimicry  which  is 


34 


WILLIAM  SHEPHERD. 


sometimes  spoken  of  as  imitation  and  which  may  be  considered 
a  reflex  adaptation  to  certain  stimuli. 

It  is  necessary  first  to  define  precisely  the  term  imitation 
as  it  is  applied  in  comparative  psychology.  The  term  imita¬ 
tion  is  used  in  a  number  of  different  senses.  First  it  is  used 
as  a  synonym  for  what  may  be  more  accurately  called  instinc¬ 
tive  imitation.  This  is  the  form  of  imitation  shown  by  all 
animals  in  the  performance  of  certain  necessary  acts,  such  as 
that  of  a  chick  when  it  pecks  at  a  bit  of  food  on  seeing 
another  chick  do  so.  A  second  use  of  the  word  is  in  relation 
to  mass  activities  and  we  may  therefore  speak  of  it  as  gre¬ 
garious  imitation.  This  form  of  imitation  is  the  performance 
of  an  act  similar  to  that  performed  by  another  animal  of  a 
herd  or  flock,  the  latter  act  being  due  to  a  definite  stimulus 
but  the  act  of  the  imitator,  although  similar  to  that  of  the 
imitatee,  is  not  produced  by  this  same  stimulus  but  by  the 
stimulus  of  seeing  or  of  hearing  the  first  animal.  This  form 
of  imitation  is  illustrated  by  a  herd  of  buffaloes  running  off 
in  alarm  or  a  flock  of  sheep  following  their  leader  and  jump¬ 
ing  over  an  imaginary  obstacle.  Lastly,  there  is  inferential 
or  reflective  imitation,  where  one  individual  sees  another 
perform  an  act,  realizes  or  understands  the  consequences  of 
that  act,  and  thereupon  performs  a  similar  act  with  the  idea 
of  getting  the  same  results. 

Of  the  above  forms  of  imitation  the  first  two  are  of  a  low 
order,  and  perhaps  no  comparative  psychologist  will  deny 
them  to  many  of  the  higher  animals  below  man.  The  con¬ 
troversy,  however,  arises  regarding  the  presence  and  the 
amount  of  the  higher  form  of  imitation,  the  imitation  that 
has  been  defined  as  inferential.  An  attempt  was  made  to 
test  the  presence  of  this  form  of  imitation,  and  three  separate 
kinds  of  tests  were  made. 

An  apparatus  and  plan  similar  to  those  already  employed 
by  Hobhouse  (12,  chap,  x),  and  by  Watson  (10,  p.  175), 
with  which  the  former  obtained  positive  and  the  latter  nega¬ 
tive  results,  were  used  by  me  in  this  work.  This  apparatus 
consists  of  a  glass  tube  or  cylinder,  15  inches  long  and  |-inch 
in  diameter,  and  a  plunger  of  wood  less  in  diameter  but 


IMITATION. 


35 


3  inches  longer  than  the  tube.  The  diameter  of  the  wooden 
plunger  was  such  that  it  could  be  readily  inserted  in  the  tube 
and  was  freely  movable.  A  piece  of  food,  usually  banana  or  a 
peanut,  placed  crosswise  in  the  tube,  was  inserted  in  the 
tube  and  pushed  down  about  half  way.  A  piece  of  food  was 
always  selected  sufficiently  large  not  to  drop  through'  the 
tube  when  the  latter  was  held  in  a  vertical  position,  and  yet 
sufficiently  small  that  it  could  be  readily  displaced  when  the 
plunger  was  used  to  push  it  through  the  tube.  This  appara¬ 
tus  was  presented  in  turn  to  eight  monkeys  and  the  imita¬ 
tion  tests  were  begun  after  each  had  failed  to  manipulate 
it  three  times.  The  tube  and  the  stick  were  placed  in 
the  cage  with  the  animal  to  see  if  he  could  push  out  the  food 
after  his  attention  had  been  attracted  and  he  had  been  shown 
by  the  experimenter  how  the  stick  was  to  be  manipu¬ 
lated  for  obtaining  the  banana  or  peanut.  I  endeavored  co 
have  the  monkeys  see  me  perform  the  act  at  least  three 
times  before  each  trial,  and  to  this  end  I  watched  carefully 
each  animal  while  the  exhibition  was  being  given.  If  there 
was  in  my  mind  any  doubt  that  the  animal  had  paid  close 
attention  to  the  performance  of  the  act  by  me,  I  repeated  it. 
Following  the  three  demonstrations  the  animal  was  given 
the  apparatus  for  one  minute,  and  this  amount  of  time  was 
allowed  him  in  which  to  perform  the  act.  In  the  case  of 
some  animals  these  tests  were  made  daily  and  in  the  case 
of  others  there  were  intervals  of  one  or  two  days.  The  varia¬ 
tion  in  the  time  routine  did  not  appear  to  have  any  influence 
upon  the  learning.  The  number  of  trials  for  each  animal 
was  also  variable,  from  24  to  96,  each  having  seen  the  act 
performed  three  times  before  each  trial,  i.e.,  having  seen  the 
act  from  72  to  288  times. 

All  the  monkeys  failed  to  show  any  signs  of  imitation,  and 
I  was  unable  to  verify  on  these  animals  results  like  those 
reported  by  Hobhouse.  At  the  end  of  the  tests  all  animals 
acted  in  much  the  same  way  as  at  the  beginning  of  the  tests 
and  the  first  notes  may  be  used  to  indicate  the  general  charac¬ 
ter  of  their  activity.  They  bit  at  the  food  in  the  tube,  looked 
into  the  end  of  the  tube  at  the  banana,  jerked  the  tube 


36 


WILLIAM  SHEPHERD. 


around,  often  took  up  the  stick  and  bit  it;  sometimes  picked 
up  the  stick  and  threw  it  away,  dropped  the  tube,  as  if  they 
gave  it  up.  While  I  was  exhibiting  the  mechanism  an 
animal  would  watch  the  operation  closely,  and  at  the  moment 
the  food  appeared  on  the  end  of  the  tube  within  the  cage,  he 
seizdd  it.  Sometimes  they  attempted  to  reach  into  the  tube 
to  get  the  food.  In  this  experiment  I  also  tried  Hobhouse’s 
plan  of  ‘suggestion.’  When  an  animal  was  wrestling  with  the 
tube  I  pointed  to  and  moved  the  stick  towards  him  to  call 
his  attention  to  it.  Thereupon,  sometimes,  an  animal  took 
up  the  stick,  but  only  to  throw  it  away  after  a  few  seconds. 
In  brief,  throughout  the  three  weeks  of  this  experiment  not 
one  of  the  animals  appeared  to  show  any  understanding  of 
the  problem,  and  any  ability  to  cope  with  it.  It  may  be 
urged  that  a  greater  number  of  trials  than  24,  the  number 
some  of  the  animals  received,  would  have  brought  success 
for  some  of  them,  but,  were  imitation  of  this  kind  an  impor¬ 
tant  and  a  constant  condition  in  monkeys,  this  number  of 
trials  would  have  been  sufficient  for  them  to  demonstrate 
its  presence. 

A  second  experiment  on  imitation  was  then  performed. 
This  experiment  was  also  similar  to  one  made  on  monkeys 
by  Hobhouse  (12,  chap,  x)  and  by  Watson  (10,  pp.  173,  174) 
A  T-rake,  consisting  of  a  light  handle  18  inches  long,  with  a 
cross  piece  4  inches  long  nailed  at  one  end,  and  at  right  angle 
to  the  handle,  was  used.  This  was  placed  with  the  handle 
end  through  the  wire  side  of  the  cage  and  with  the  T-end 
extending  outward  on  the  floor  of  the  room.  A  piece  of 
banana  or  a  peanut  was  placed  on  the  floor  outside  the  cage 
but  within  the  sweep  of  the  rake  when  handled  by  an  animal 
inside  the  cage.  In  this  experiment  I  wished  to  see  if  the 
monkeys  could  grasp  the  situation  of  the  use  of  the  rake. 
Two  separate  factors  of  adjustment  enter  into  this;  first, 
the  use  of  the  rake  for  the  use  of  grasping  or  reaching  out 
towards  the  food,  and,  secondly,  the  use  of  the  implement  to 
draw  the  food  nearer  the  cage  and  within  reach  of  the  hand 
itself. 

Monkeys  i,  2,  3,  4,  5,  6,  7  and  8  were  tested  in  this  manner. 


IMITATION. 


37 


I  showed  an  animal,  by  hooking  the  T  around  the  food  and 
pushing  the  rake  forward,  but  necessarily  from  the  outside 
of  the  cage,  three  times  before  each  trial.  I  then  let  the 
animal  try  the  apparatus  for  two  minutes.  Each  of  the 
eight  animals  was  given  from  24  to  120  trials  in  the  four  weeks 
these  experiments  were  continued.  Each  animal  had  failed 
to  use  the  rake  three  times,  without  being  shown,  before  the 
imitation  tests  were  begun. 

Monkeys  i,  2,  4,  5,  6,  8,  failed  as  completely  as  in  the  pre¬ 
vious  experiment.  Each  seized  the  end  of  the  rake  handle 
within  the  cage,  jerked  it  around,  bit  it,  tried  to  reach  the 
food  with  their  hands  through  the  wire  of  the  cage.  Some¬ 
times  they  became  angry  and  threw  the  rake  aside;  in  some 
cases  they  finally  gave  it  up.  I  noted,  however,  that  all  soon 
came  to  pull  the  rake  into  the  cage,  up  to  the  T,  which  was 
as  far  as  the  wire  of  the  cage  would  permit.  So  far  as  I  could 
tell,  each  animal  watched  me  closely  while  I  was  showing 
them,  appeared  to  have  much  interest  in  the  proceedings,  and 
seized  the  food  through  the  wire  of  the  cage  the  moment  it 
was  within  reach.  But  what  the  six  monkeys  did  not  do  was 
to  push  the  rake  out  and  hook  the  cross  piece  around  the 
food.  In  all  of  the  trials  with  these  six  monkeys  so  far  as  I 
could  see,  none  gave  a  sign  of  using  the  rake  as  a  tool  with 
which  to  draw  the  food  toward  the  cage.  Here  again  it 
may  be  urged  that  a  greater  number  of  trials  than  24  should 
have  been  given  to  all  animals,  but  the  simplicity  of  the 
apparatus  was  such  that  in  a  child  of  the  same  age  one  or 
two  trials  are  sufficient  for  a  successful  imitation. 

After  several  days  tests  with  two  of  the  animals,  3  and  7, 
there  appeared  some  evidence  of  imitation.  Monkey  3 
learned  to  push  out  the  rake,  and,  with  much  slashing  about 
of  the  T  end,  would  draw  in  the  food.  The  securing  of  the 
food  by  hooking  the  T  around  it  was,  however,  very  awkward 
work  for  her.  Sometimes  she  would  knock  the  peanut  away 
in  her  effort  to  pull  it  in.  On  its  being  replaced  by  me  she 
usually  succeeded  in  drawing  it  in  roughly.  The  best  that 
can  be  said  of  her  performance  is  that  she  appeared  to  learn  to 
imitate  me  perfectly  in  pushing  the  rake  out,  and  awkwardly 
in  pulling  the  food  in  with  the  rake. 


38 


WILLIAM  SHEPHERD. 


Following  is  an  account  of  the  tests  on  the  third  day.  It 
will  be  remembered  that  the  method  of  securing  the  food  by 
the  use  of  the  rake  was  demonstrated  three  times  before  each 
test.  On  this  day,  however,  this  demonstration  was  omitted 
after  the  seventh  test.  Trial  i  was  a  failure;  the  animal  did 
not  attempt  to  take  hold  of  the  rake  after  being  shown  three 
times.  On  the  second  trial,  however,  after  the  three  dem¬ 
onstrations,  the  animal  grasped  the  rake,  and  moved  it 
about  in  the  direction  of  the  food.  She  succeeded  in  bring¬ 
ing  in  the  nut  sufficiently  far  so  that  she  reached  it  and  ate 
it;  time,  85  seconds.  In  this  first  successful  attempt  she 
grasped  the  rake  awkwardly  and  did  not  at  first  seem  able 
to  manage  it,  but  eventually  she  managed  to  swing  it  around 
so  that  the  nut  was  caught  and,  as  has  been  said,  pulled  in 
the  nut  so  that  she  secured  it  by  reaching  through  the  bars 
of  the  cage.  In  the  next  trial  the  movements  of  handling 
the  rake  were  about  the  same  as  those  in  the  preceding  trial, 
although  she  had  acquired  some  facility  in  the  use  of  the  tool, 
and  managed  to  secure  the  nut  in  29  seconds.  On  the 
fourth  trial,  during  the  demonstration  she  took  hold  of  the 
rake  and  pushed  it  outwards  toward  the  food.  After  this 
demonstration  she  pushed  the  rake  outwards  in  an  apparently 
purposeful  manner  and  secured  the  nut  in  20  seconds.  The 
fifth  trial  was  similar  to  the  fourth,  but  with  an  increasing 
ease  in  adjustment  and  with  apparent  greater  facility  in  the 
use  of  the  rake.  In  8  final  trials  on  this  day  the  demonstra¬ 
tions  were  omitted  but  the  actions  of  the  animal  were  similar 
to  those  mentioned  in  connection  with  the  fourth  and  fifth 
trials.  On  the  sixth  and  tenth  trials  the  manipulation  of  the 
rake  caused  the  nut  to  roll  further  away  from  the  cage  and 
each  time  I  replaced  it.  The  times  for  these  8  trials  were 
respectively:  15,  15,  9,  12,  24,  14,  4  and  8  seconds. 

Three  days  later,  the  fourth  day  of  the  tests,  demonstra¬ 
tions  were  given  in  the  first  and  second  tests.  The  results, 
however,  were  similar  to  those  on  the  third  day,  but  with 
shortened  times  for  the  performance  of  the  act.  The  times 
were  as  follows :  10,  8,  3,  4,  2,  6,  7,  9,  5,  4,  3,9,2,  and  2  seconds. 
On  the  seventh  trial  she  managed  to  get  the  nut  only  part 


IMITATION. 


39 


way  with  the  first  pulling  movement,  but  then,  with  apparent 
intention,  she  gave  another  pull  and  brought  the  nut  within 
reach.  On  the  thirteenth  trial  the  nut  rolled  away  when 
touched  with  the  rake  but  the  animal  pushed  the  rake  out 
farther  beyond  the  nut  and  managed  to  secure  it  in  the  usual 
way. 

Monkey  7  had  failed  to  show  evidence  of  imitation  on  six 
days  of  3  trials  each  when  I  manipulated  the  rake  and  at¬ 
tempted  to  exhibit  the  mechanism  of  securing  food.  It  was 
thought  that  the  operation  of  another  animal  might  be  imi¬ 
tated,  and  for  this  reason  I  placed  her  with  monkey  3,  which 
at  that  time  had  learned  to  use  the  rake  with  facility.  In 
these  experiments  I  carefully  watched  monkey  7  in  order 
to  be  reasonably  certain  that  she  observed  monkey  3  perform 
the  act  with  the  rake.  Only  after  I  was  sure  the  animal 
had  been  looking  in  the  direction  of  monkey  3  while  the  latter 
performed  the  act  three  times  did  I  begin  a  test  of  monkey 
7.  At  these  times  also  I  called  attention  to  the  tool  by 
pointing  to  it  and  to  the  food.  In  each  trial  she  was  per¬ 
mitted  two  minutes  to  perform  the  imitation  act,  and  if  it 
was  not  performed  in  that  time  I  counted  the  test  a  failure. 
The  first  five  tests  were  failures,  and  likewise  the  seventh 
and  tenth.  On  the  sixth  trial  she  pushed  the  rake  outwards 
awkardly,  but  with  such  movements  that  she  could  not 
secure  the  food.  Finally,  however,  after  79  seconds,  she 
managed  to  hook  the  cross  pieces  about  the  food  and  immedi¬ 
ately  pulled  it  in.  The  eighth  and  ninth  trials  were  similar 
to  the  sixth  but  the  food  was  secured  in  20  and  8  seconds 
respectively.  The  tenth  trial  I  have  counted  a  failure,  for 
in  this  case  the  animal  pushed  out  the  rake  and  pulled  it  in 
but  did  not  manage  to  get  the  cross  piece  hooked  around  the 
food.  In  the  two  minutes  allowed  for  the  performance  of 
the  act,  she  did  not  manage  to  secure  the  food. 

On  the  second  day  of  these  tests  she  failed  to  show  by  her 
actions  any  evidence  of  imitation  in  the  second,  third,  sixth, 
ninth  and  tenth  trials.  Only  ten  seconds  were  required  for 
the  proper  performance  of  the  act  on  the  first  trial,  for  she 
immediately  manipulated  the  rake  so  that  it  caught  the  nut 


40 


WILLIAM  SHEPHERD. 


and  she  pulled  it  inwards.  The  fourth,  fifth  and  seventh 
trials  were  similar,  12,  15  and  9  seconds  respectively.  Al¬ 
though  the  eighth  trial  was  counted  a  failure  the  monkey 
did  manipulate  the  rake  properly,  but  in  pushing  it  out¬ 
wards  the  nut  was  hit  and  rolled  farther  way.  In  the  final 
trials  of  this  day  the  animal  did  not  make  many  efforts  to 
use  the  rake,  although  two  minutes  were  allowed.  In  these 
experiments  the  movements  of  pushing  the  rake  outwards 
were  well  performed,  but  those  of  pulling  inwards  were  very 
badly  executed.  This  was  also  noted  on  the  following  day, 
when  in  6  trials,  she  managed  to  secure  the  food  four  times, 
in  17,  9,  II  and  5  seconds.  In  subsequent  trials  she  con¬ 
tinued  to  be  incoordinate  in  the  pulling  in  movements,  but 
accurate  in  pushing  out  the  rake. 

It  may  be  said  that  monkey  7  did  not  make  the  mental 
connection  between  seeing  me  manipulate  the  rake  and  the 
idea  of  the  acquisition  of  food,  but  that  some  connection  or 
association  was  formed  between  seeing  monkey  3  perform 
the  act  and  such  an  idea  (or  what  corresponds  to  an  idea  in 
the  monkey  mind).  The  impulse  to  handle  the  rake,  to 
manipulate  it  and  to  use  it  in  connection  with  food  may  prop¬ 
erly  be  said  to  be  due  to  her  having  seen  monkey  3  obtain 
food  by  the  use  of  this  tool.  This  impulse  or  association 
may  be  explained  as  A,  ideal,  or  B,  imitative.  In  the  present 
state  of  comparative  psychology  it  is  best  to  consider  it  the 
latter,  and  we  conclude  that  the  use  of  the  rake  by  monkey 
7  has  been  due  to  an  imitative  impulse,  the  tendency  to  per¬ 
form  the  same  or  a  similar  act  performed  by  another. 

In  a  third  experiment  to  test  the  ability  to  imitate  the 
apparatus  used  in  a  previous  test  of  analogical  reasoning  was 
again  employed.  A  piece  of  banana  was  suspended  from  a 
pole  that  extended  across  the  room.  The  food  was  placed 
about  4  feet  from  the  floor,  high  enough  to  be  beyond  the 
reach  of  the  animal  when  it  stood  upright  on  the  floor.  A 
light  pole,  9  feet  long,  1.5  inches  in  diameter,  was  loosely 
attached  at  one  end  by  means  of  a  pivot  to  a  support  and 
extended  7  feet  across  the  open  space  of  the  room  to  a  hori¬ 
zontal  supporting  board  (C),  which  was  2.5  feet  from  the 


IMITATION. 


41 


floor.  Figure  2  shows  the  arrangement.  On  the  horizontal 
board  the  free  end  of  the  pole  was  easily  moved,  and  by 
shifting  it  to  the  position  P-X  the  pole  was  brought  under 
the  suspended  food.  To  bring  about  this  change  it  was 
necessary  to  move  the  free  end  of  the  pole  about  3  feet,  with 
corresponding  decreases  in  the  amount  of  movement  the 
nearer  to  the  pivot  the  pole  was  grasped.  In  the  position 
P-X  the  animal  was  able  to  reach  the  food  if  it  climbed  upon 
the  pole.  The  problem  for  the  animal  was  to  slide  the  free 
end  of  the  pole  sufficiently  far  on  the  horizontal  board  or 


Fig.  2.  Diagram  of  apparatus  used  in  tests  of  reason  and  of  imitation.  A,  sus¬ 
pended  banana;  B,  sliding  pole  in  original  position;  PX,  position  to  which  pole  had 
to  be  moved  in  order  that  the  animal  might  reach  the  food;  C,  supporting  slide. 


slide,  to  bring  the  pole  under  the  suspended  food :  to  go  upon 
the  pole  and  get  the  food  by  reaching  upwards  about  10  inches. 

Monkey  3  had  been  tested  with  this  apparatus  in  a  series 
of  experiments  on  analogical  reasoning  (see  p.  52  ff.)  and 
had  failed  to  manipulate  it.  In  this  first  test  she  was  not 
shown  how  to  manipulate  it,  but  was  shown  when  the  ex¬ 
periments  on  imitation  were  begun.  Before  each  test  by  the 
animal  I  moved  the  pole  from  its  original  position  to  that 
of  P-X  and  permitted  the  animal  to  obtain  the  food  each 
time.  After  having  been  shown  in  these  three  trials  that  the 
moving  of  the  pole  was  essential  for  the  securing  of  food  I 
allowed  two  minutes  in  which  the  animal  might  perform  the 


42 


WILLIAM  SHEPHERD. 


act.  If  the  act  was  not  accomplished  in  that  time  I  called 
the  test  a  failure  and  repeated  the  demonstrations.  On  the 
first  day  of  this  experiment  she  succeeded  in  performing  the 
complex  adjustment  of  pole,  etc.,  four  out  of  eight  times. 
On  the  first  trial  she  moved  the  pole  awkwardly,  but  suffi¬ 
ciently  far  that  she  was  able  to  reach  the  food ;  30  seconds. 
On  the  second  trial  she  moved  the  pole  only  a  trifle  at  first, 
but  returned  to  it  and  succeeded  in  moving  it  the  required 
distance;  25  seconds.  On  the  next  trial  she  changed  the 
movement  of  pushing  to  that  of  lifting  the  pole  and  pushing 
at  the  same  time.  In  this  her  movements  were  awkward 
but  she  managed  to  get  the  food  in  45  seconds.  The  next 
three  trials  were  counted  as  failures,  although  in  all  of  them 
the  animal  manipulated  the  pole  and  showed  signs  of  recogni¬ 
tion  of  the  use  to  which  the  pole  was  to  be  put.  On  the  fourth 
trial  after  having  moved  the  pole  a  short  distance  and  not 
obtaining  food,  she  tried  to  get  the  food  by  going  to  the  cross 
piece  from  which  the  food  was  suspended.  On  the  fifth 
trial  she  pushed  the  pole  off  the  slide,  and  could  not  get  the 
food.  On  the  sixth  trial  she  moved  the  pole  a  short  distance, 
and  refused  to  complete  the  act.  On  the  seventh  trial  she 
moved  the  pole  sufficiently  far  to  obtain  the  food,  20  seconds; 
but  on  the  eighth  trial  she  did  not  try  to  move  the  pole  or  to 
obtain  the  food. 

On  the  following  day  she  was  not  shown  how  to  manipu¬ 
late  the  apparatus  the  first  three  trials,  two  of  which  were 
successful,  but  was  shown  on  the  other  seven  trials.  At  first 
she  pulled  the  pole  part  way,  but  it  appeared  to  be  difficult 
work,  and  she  obtained  the  food  in  20  seconds.  The  second 
trial  she  pulled  the  pole  about  6  inches  and  stopped;  I  took 
hold  of  the  pole  and  helped  her  to  move  it  a  few  inches,  and 
then  she  made  a  great  effort  and  pulled  the  pole  sufficiently 
far  to  obtain  the  food.  The  third  trial  she  did  not  attempt 
to  move  the  pole.  The  following  seven  trials  were,  it  has 
been  mentioned,  preceded  by  three  demonstrations  each. 
In  only  the  fourth  trial  did  she  take  hold  of  the  pole,  at  other 
times  she  did  not  attempt  any  manipulation.  On  the  third 
day  of  the  tests,  six  days  following  that  just  mentioned,  she 


IMITATION. 


43 


failed  to  manipulate  the  apparatus  in  six  trials,  although  she 
was  shown  three  times  before  each  trial.  Only  once  on  this 
day  did  she  touch  the  poll.  Two  days  later,  she  failed  on 
the  first  six  trials.  On  the  seventh  she  helped  me  to  push 
the  pole  when  I  was  demonstrating  it,  and  following  this 
she  managed  to  get  the  pole  moved  by  her  own  efforts  in  68 
seconds.  On  the  eighth  trial  she  moved  the  pole  part  way 
and  obtained  the  food  in  30  seconds.  The  ninth  trial  was 
a  failure  in  two  minutes.  Seven  days  later  she  was  given 
three  trials  and  was  not  shown  how  to  manipulate  the  appara¬ 
tus.  She  did  not  exhibit  any  signs  of  ability  to  manipulate 
the  apparatus  and  was  then  shown.  The  fourth  trial  was  a 
failure;  on  the  fifth,  she  took  hold  of  the  pole  at  the  time  I 
was  moving  it,  and  after  the  demonstrations  she  immediately 
attempted  to  move  the  pole,  which  she  managed  in  36  seconds. 
On  the  sixth  trial  she  managed  to  get  the  food  in  26  seconds. 
The  seventh  trial,  18  seconds,  and  the  eighth  trial  in  9  seconds 
were  successful.  In  the  remaining  17  trials  on  this  day 
she  gradually  lowered  the  time  for  the  .performance  of 
the  act  although  her  actions  were  always  about  the  same. 
Two  days  later  there  were  no  failures  in  20  trials,  but  the 
actions  of  the  animal  in  2  of  the  trials  were  noteworthy. 
In  these  trials  the  monkey  moved  the  pole  part  way,  then 
stopped,  and  appeared  to  be  observing  the  amount  of  the 
movement  and  making  a  judgment  regarding  the  possibility 
of  reaching  the  food  from  the  pole  in  the  position  in  which 
she  had  placed  it.  Then,  not  liking  the  position  she  moved 
the  pole  farther  and  climbed  upon  it  and  obtained  the  food. 

In  these  tests  there  was  a  gradual  learning  to  eliminate 
unnecessary  movements  and  to  perform  the  necessary  move¬ 
ments  in  a  satisfactory  manner.  The  experiment  does  not, 
however,  wholly  belong  to  the  type  of  learning  of  trial  and 
error,  for,  as  has  been  remarked,  the  monkey  moved  the  pole 
properly  the  first  time  she  attempted  to  do  so.  There  was 
no  previous  groping  for  a  something,  no  fumbling  with  any¬ 
thing  but  the  pole.  The  attention,  so  far  as  shown  in  action 
was  directed  to  the  pole.  There  was  an  immediate  grasp 
of  the  situation,  and  this  coming  after  she  had  been  shown 


44 


WILLIAM  SHEPHERD. 


that  the  food  was  to  be  reached  by  changing  the  position  of 
the  pole  is  taken  as  evidence  of  imitation.  The  fact  that  in 
later  tests  she  failed  to  pay  attention  to  the  pole  and  to 
attempt  to  move  it  does  not  mean  that  she  could  not  imitate, 
but  it  is  well  known  that  the  monkey  is  extremely  variable  in 
its  actions,  and  its  attention  is  held  with  difficulty.  We  know 
that  in  the  production  of  habit,  as  many  observers  have 
pointed  out,  there  is  not  a  gradual  shortening  of  the  time  of 
reaction  as  in  the  case  of  cats  and  dogs,  but  that  the  time  for 
the  performance  of  an  act  is  extremely  variable.  It  is  this 
factor  of  variability  due  to  elements  such  as  lack  of  hunger, 
etc.,  which  seems  to  me  to  account  for  the  lack  of  attention 
to  the  problem.  It  is  further  to  be  noted  that  in  the  success¬ 
ful  trials  she  used  a  variety  of  means  for  the  accomplishment 
of  the  end;  sometimes  she  pushed  the  pole  unhesitatingly 
through  the  required  distance;  at  times  she  pulled  it,  and  at 
times  she  pulled  and  pushed  it.  The  variety  of  action  indi¬ 
cates  that  the  performance  of  the  act  is  not  like  that  of  a  habit 
formation,  but  that  of  attempting  to  accomplish  an  object 
in  any  manner  that  this  could  be  done.  The  performance 
of  the  act  was  awkward,  but  there  appeared  to  be  imitation 
of  a  relatively  high  order. 

In  the  experiments  that  have  been  described  evidence  of 
imitation  by  monkeys  3  and  7  was  found  in  the  second  experi¬ 
ment  of  the  series.  These  two  monkeys  and  the  other  six 
failed  to  show  signs  of  imitation  in  the  first  experiment  and  I 
failed  to  find  any  signs  of  imitation  on  the  part  of  the  six 
monkeys  in  the  second  experiment.  When  these  results  are 
combined,  I  think  they  indicate  in  a  general  way  that  some 
monkeys  may  and  do  learn  by  imitation.  The  amount  of 
imitation  is  not  shown,  but  the  fact  that  in  so  many  simple 
experiments  negative  results  were  obtained  indicates  that 
these  animals  do  not  imitate  to  the  extent  that  has  been 
ascribed  to  them.  We  are,  I  believe,  justified  in  concluding 
that  imitation  is  a  mental  function  of  the  monkey  or  of  some 
monkeys,  although  the  results  of  my  experiments  may  be 
interpreted  to  mean  that  imitation  does  not  play  a  very 
important  part  in  their  learning  process. 


IDEA  TION. 


45 


Ideation . 

The  evolution  and  anecdote  schools  attribute  ideation  of 
a  comparatively  high  order  to  the  animals  with  brains  similar 
to  that  of  man,  and  they  hold  that  ideas  similar  to  those  of 
man  play  an  important  part  in  animal  behavior.  They  base 
this  belief,  however,  upon  uncontrolled  observation  and  upon 
flimsy  and  circumstantial  evidence  and  not  upon  controlled 
experiments  and  unequivocal  facts.  The  evolutionists  also 
appear  to  believe  it  necessary  to  attribute  ideas  to  animals, 
else  the  doctrines  of  a  progressive  mental  development  would 
not  coincide  with  that  of  the  physical  development.  On  the 
other  hand,  others,  mainly  experimenters,  hold  that  the 
casual  observations  do  not  indicate  animal  ideation  and  the 
same  facts  are  interpreted  differently.  Special  tests  have 
given  negative  results  and  from  these  and  from  the  careful 
observation  of  animals  in  laboratory  surroundings  they  con¬ 
clude  that  animal  ideation  is  not  proven,  and  that  the  present 
evidence  tends  to  indicate  an  absence  or  a  lack  of  ideas  in 
the  animal  mind.  Some,  however,  are  willing  to  admit  that 
animals  may  have  ideas,  although  in  small  number,  but  are 
forced  to  conclude  that  ideas  are  a  very  unimportant  element 
in  minds  below  that  of  man.  It  is  true  that  for  the  most 
part  the  experiments  of  these  men  have  not  been  special 
tests  for  ideation,  but  tests  for  other  reactions  in  which  idea¬ 
tion,  if  present,  should  or  might  have  been  exhibited. 

Before  passing  to  the  evidence  of  ideation,  it  seems  well 
to  define  the  term  ‘idea’  and  thus  to  have  a  precise  notion 
of  what  we  should  look  for  in  animal  behavior.  For  the  pur¬ 
pose  of  comparative  psychology  an  idea  may  be  defined  in 
the  following  ways:  a,  an  image  or  picture  of  a  visual  object 
which  is  formed  by  the  mind;  h,  a  general  notion  or  concep¬ 
tion;  c,  a  plan  or  purpose  of  action  or  an  intention;  d,  idea  in 
the  sense  of  an  understanding  of  a  certain  relation  or  situa¬ 
tion  (as  of  sensible  objects).  If,  therefore,  an  animal  ex¬ 
hibits  any  of  the  mental  conditions  noted  above  we  may 
conclude  that  ideation  is  present. 

A  simple  test  for  ideation  was  made  with  animals  i,  2 


46 


WILLIAM  SHEPHERD. 


and  3.  A  board  20  inches  long  and  3|-inches  wide  was 
placed  with  one  end  against  the  side  of  the  cage  and  within 
reach  of  the  animal  with  the  other  end  extending  outwards 
from  the  cage  and  beyond  reach.  Food  was  placed  at  the 
farther  end.  The  object  of  the  tests  was  to  determine  if  an 
animal  would  understand  the  situation  and  be  able  to  secure 
the  food  by  the  indirect  method  of  pulling  at  the  board  near 
the  cage  rather  than  by  directing  its  efforts  at  the  food  or 
the  food  end  of  the  board  which  was  beyond  reach.  In  the 
first  trial  monkey  3  after  some  testing  of  the  openings  of  the 
wire  netting,  seized  the  board  awkwardly  near  the  end  with¬ 
in  reach,  pulled  the  board  alongside  the  cage  and  secured 
the  food,  30  seconds.  In  this  trial  the  attention  for  only  a 
few  seconds  was  directed  to  the  food  position  but  was  directed 
mainly  to  the  end  of  the  board  that  did  not  contain  the  food. 
The  actions  of  the  animals  in  manipulating  the  board  were 
awkward  but  only  in  the  method  of  reaching  for  and  hand¬ 
ling  it.  The  actions  were  directed  to  the  board,  and  not  to 
the  food,  and  it  appears  that  here  is  an  example  of  an  under¬ 
standing  of  a  situation,  a  direction  of  action  to  an  end  not  of 
special  interest  in  the  situation.  In  the  second  and  third 
performances  she  duplicated  her  actions,  but  with  shorter 
times  for  its  accomplishment  because  the  awkwardness 
largely  disappeared  and  because  the  preliminary  direction 
of  attention  to  the  food  was  absent,  20  and  10  seconds.  In 
later  tests  she  continued  to  react  with  complete  success, 
reducing  the  time  to  three  seconds  in  the  fifth  trial,  which 
time  includes  that  for  the  manipulation  of  the  board  and  the 
securing  of  the  food.  Monkey  i  succeeded  In  the  third 
trial  but  showed  more  misdirected  efforts  than  did  monkey 
3.  The  third  animal  also  managed  to  perform  the  necessary 
acts  to  secure  the  food  in  the  third  trial,  but  the  actions  were 
more  awkward  and  poorly  directed  than  those  of  monkeys 
I  and  3, 

At  the  beginning  of  this  test  there  were  many  unnecessary 
movements  on  the  part  of  each  animal,  but  this  awkward¬ 
ness  or  lack  of  understanding  of  how  to  deal  with  the  situa¬ 
tion  was  mainly  that  of  motor  adjustment.  It  was  a  diffi- 


IDEATION. 


47 


culty  in  dealing  with  the  board  through  the  wire  netting  of 
the  cage  and  not  a  difficulty  or  a  lack  of  understanding  of 
the  problem,  viz.,  of  reaching  for  and  of  manipulating  the 
board.  In  the  first  trial  of  monkey  3  the  animal  directed 
its  attention  to  the  board  near  the  cage,  and  showed  that 
it  appreciated  the  relation  between  this  part  of  the  board 
and  the  securing  of  food.  The  later  reduction  in  time  for 
the  performance  of  the  act,  which  at  first  sight  makes  the 
experiment  appear  to  be  only  another  instance  of  learning 
by  trial  and  error,  was  mainly  that  of  a  proper  adjustment 
of  arms  and  hands  to  the  wire  netting  and  not  that  of  attack¬ 
ing  the  board  at  the  proper  place. 

These  results  indicate  the  presence  of  ideas  of  the  above 
described  third  or  fourth  class,  i.e.,  a  plan  of  action  or  an 
understanding  of  a  situation.  It  was  apparent  that  from 
the  first  the  animal  understood  that  the  food  could  not  be 
reached  directly  but  must  be  obtained  by  an  indirect  attack 
on  some  other  part  of  the  apparatus.  There  was  in  this 
case  no  general  activity  such  as  has  been  described  by  numer¬ 
ous  investigators  in  connection  with  the  puzzle  box  experi¬ 
ments;  the  trying  here  and  the  pulling  there  were  notably 
absent,  and  the  attention  of  the  animal  was  concentrated  on 
the  board  and  on  the  getting  the  food.  For  a  few  seconds 
after  the  board  and  food  were  displayed  the  hungry  animal 
would  reach  in  vain  for  the  food  which  was  beyond  its  reach, 
but  this  unsuccessful  method  was  given  up  and  the  attack 
directed  to  the  board  on  which  the  food  was  placed.  It  is 
also  of  great  importance  to  note  that  the  attack  was  directed 
not  to  the  part  of  the  board  on  which  the  food  was  placed, 
but  to  the  part  of  the  board  away  from  the  food. 

The  simplicity  of  the  situation  may  be  urged  as  an  argu¬ 
ment  against  the  presence  of  ideation  in  solving  the  problem, 
but  I  would  again  call  attention  to  the  ordinarily  complex 
character  of  similar  experiments  that  have  given  negative 
results  to  other  observers.  In  such  experiments  we  must 
steer  clear  of  both  an  absolute  simplicity  and  of  a  complexity 
abnormal  to  the  animal.  We  must  test  the  animal  under 
conditions  which  are  within  ks  mental  range  and  which  will 


48 


WILLIAM  SHEPHERD. 


show  the  ability  to  reason.  It  is  equally  bad  to  set  impossible 
conditions  and  to  draw  unsupported  conclusions,  and  in 
both  these  ways  comparative  psychologists  have  attempted 
to  solve  the  problem  of  animal  reason  and  ideation.  To 
conclude,  for  example,  that  a  dog  or  a  monkey  possesses 
no  power  of  ideation  or  of  reasoning  because  it  does  not 
thread  a  needle  when  the  needle  and  thread  are  supplied 
or  because  it  does  not  unlock  a  door  when  the  key  is  pre¬ 
sented  is  to  limit  the  terms  ideation  and  reason  to  the 
ability  to  perform  certain  activities  connected  with  a  certain 
class  of  civilized  man.  The  examples  cited  are,  perhaps, 
extremes  but  they  illustrate  the  attitude  of  a  certain  class 
of  experimentalists.  On  the  other  hand,  to  conclude  that 
a  cat  reasons  because  it  attracts  attention  by  scratching  on 
the  window  pane  or  because  it  manages  to  strike  an  electric 
button  for  the  opening  of  the  door  is  to  take  no  account  of 
the  possibility  of  previous  training  of  the  nature  of  trial  and 
error.  We  should  steer  between  the  two  extremes  and  test 
the  so-called  higher  powers  of  animals  by  presenting  to  them 
conditions  appropriate  to  the  class.  In  the  simple  experi¬ 
ment  described  in  this  section  and  in  others  to  be  described 
in  the  section  on  reasoning  (p.  52  ff.)  the  conditions  are  appro¬ 
priate  to  the  monkey  family.  We  have  presented  to  the 
animal  a  new  problem  which  it  must  solve,  a  set  of  condi¬ 
tions  to  be  dealt  with  in  order  that  a  resultant  pleasure 
(hunger  satisfaction)  ensue.  In  the  solution  of  the  problem 
the  animals  took  a  direct  path.  There  was  none  of  the  fum¬ 
bling  or  groping,  no  trying  here  and  there,  no  attempts  upon 
other  parts  of  the  cage  or  its  surroundings,  but  a  direct 
attack  upon  the  board  that  held  the  food. 

Somewhat  similar  actions  were  observed  and  noted  above 
in  connection  with  the  food  box  experiments.  After  the 
previously  ignorant  (so  far  as  the  food  box  is  concerned) 
monkeys  had  been  fed  from  the  food  box  a  few  times  so  they 
might  become  acquainted  with  the  location  of  the  food,  the 
doors  were  closed.  Then  began  an  attack  upon  the  doors, 
not  upon  the  wire  netting  of  the  sides  of  the  cage.  The 
animals  remained  active  about  t3he  doors  of  the  food  boxes; 


IDEATION. 


49 


they  did  not  sit  sulkily  upon  the  platform  in  the  cage;  the 
attention  was  directed  to  the  doors  of  the  food  boxes.  Thorn¬ 
dike  indicates  a  belief  that  the  attention  of  his  cats  was 
directed  to  the  string  or  to  the  button  because  the  movement 
in  connection  with  these  parts  of  the  appliances  was  followed 
by  a  pleasure.  With  my  monkeys,  however,  the  attention 
of  the  animals  could  not  have  been  directed  to  the  doors  of 
the  food  boxes  on  account  of  a  pleasure  in  connection  with  a 
movement,  for  the  animals  did  not  have  to  perform  any 
movements  (except  those  of  taking  the  food  from  the  boxes) 
in  the  neighborhood  of  the  food  boxes,  and  in  connection  with 
the  doors  there  were  no  movements  to  be  performed.  In 
these  cases  there  was  no  activity  in  the  region  of  the  food 
boxes  or  of  the  doors  which  could  become  associated  with  a 
pleasure.  The  attention  must  then  be  due  to  something 
different  from  the  movement-pleasure  association;  and  it 
seems  probable  that  there  is  some  form  of  ideation  to  account 
for  it. 

In  the  brightness  tests  interesting  behavior  on  the  part  of 
monkey  3  was  observed.  As  has  been  explained  above,  the 
doors  were  opened  by  turning  a  button  and  thus  food  was 
secured.  After  several  days’  experiments  monkey  3  began 
to  close  the  door  of  her  own  accord  instead  of  waiting  for 
me  to  close  it  preparatory  to  another  trial.  Before  I  could 
close  the  door  after  she  had  opened  it  she  would  close  it. 
This  would  expedite  the  getting  of  food.  It  soon  became 
almost  an  habitual  custom  for  her  to  close  the  door,  and  in 
the  remaining  tests  she  did  so  from  three  to  ten  times  each 
day  throughout  the  experiments.  Why  should  an  animal 
close  the  door  if  it  was  not  with  some  design  or  intention 
(perhaps  vague)  of  hurrying  the  food-getting  process?  It 
seems  too  parsimonious  and  even  inadequate  to  call  this 
kind  of  reaction  a  mere  reflex.  In  the  puzzle  box  experi¬ 
ment  the  same  animal  and  two  others,  monkeys  i  and  2, 
often  attempted  to  hold  open  the  door  with  their  hands  and 
this  kind  of  action  was  recorded  many  times  throughout  the 
series.  At  first  I  was  inclined  to  consider  this  action  as  a 
reflex  but  it  is  overworking  the  meaning  of  the  term  reflex 


50 


WILLIAM  SHEPHERD. 


to  use  it  to  explain  or  to  describe  the  actions  of  the  three 
animals  in  this  particular.  Somewhat  similar  behavior  in  a 
different  situation  was  also  noted  with  monkey  8.  In  test¬ 
ing  his  color  discrimination  with  colored  rice  and  breads,  the 
food  was  placed  on  a  block  about  a  foot  away  from  the  cage 
and  then  moved  close  to  the  cage  so  that  he  could  readily 
reach  the  food  through  the  wire  netting.  When  the  food  was 
taken  or  rejected  the  block  was  moved  backwards  a  short 
distance  preparatory  to  placing  food  upon  it  for  another 
trial.  During  the  first  few  experiments  he  acted  as  most 
of  the  monkeys  do,  viz.,  moved  away  from  the  side  of  the 
cage  as  soon  as  the  food  was  obtained.  After  he  had  learned 
to  discriminate  the  colors,  however,  it  was  noted  that  he 
began  to  push  the  block  away  after  having  taken  the  appro¬ 
priate  food.  This  he  continued  to  do  during  the  remaining 
trials  on  that  day.  The  actions  of  monkey  8  in  this  case 
had  all  the  appearances  of  an  understanding  of  the  situation 
and  a  desire  to  hurry  the  getting  of  food.  It  is  of  consider¬ 
able  importance  in  this  connection  to  bear  in  mind  that  the 
performance  of  this  action  was  sudden  and  not  a  gradual 
growth  and  not  the  result  of  trial  and  error. 

The  actions  of  the  three  animals  in  the  situation  of  the 
diagonally  placed  board,  the  actions  of  monkey  3  in  closing 
the  door  of  the  food  box  and  the  actions  of  monkey  8  in  push¬ 
ing  away  the  block  on  which  food  was  placed  have  a  similar 
appearance.  Were  we  not  obsessed  by  the  law  of  parsimony 
we  would  immediately  say  that  these  actions  show  the 
presence  of  ideas  in  these  animals,  ideas  of  the  highest  form. 
We  are,  however,  in  keeping  with  the  law  of  parsimony,  quite 
justified  in  saying  that  the  actions  indicate  the  presence  in 
the  minds  of  the  animals  of  a  something  very  much  like  an 
idea  in  the  human  sense,  a  something  that  has  for  the  animal 
a  function  or  a  use  similar  to  an  idea  in  man.  This  ‘some¬ 
thing’  may  be  crude  and  simple,  and  doubtless  it  is  analyzed 
by  the  animal,  but  it  serves  practical  purposes.  These 
somethings  may  be  termed,  as  does  Hobhouse,  practical 
ideas;  they  may  be  partly  sensory-motor  reactions,  and  may 
be  partly  instinctive,  and  in  part  they  may  be  accounted  for 


REASONING. 


51 


by  the  superior  equipment  of  the  monkey  in  coordinated 
vision  and  in  the  use  of  the  hands.  The  evidence  of  the 
ability  to  imitate  supports  the  view  of  the  presence  of  these 
practical  ideas,  and  in  the  section  of  this  paper  on  adaptive 
intelligence  (p.  54  ff.)  will  be  found  additional  evidence. 
The  fact  that  only  a  few  of  the  animals  exhibited  anything 
like  the  actions  described,  and  each  animal  only  a  few,  indi¬ 
cates  that  these  ‘practical  ideas’  play  a  subordinate  and  unim¬ 
portant  role  in  the  ordinary  life  of  the  animal,  but  they  do 
indicate  that  ideas  may  be  present  and  have  effect  under 
certain  circumstances. 

Reasoning. 

It  was  formerly  held  that  man  alone  possesses  reasoning 
power;  other  animals  only  instinct.  Comparative  psy¬ 
chology  has  modified  the  older  view  of  instinct,  viz.,  that  it 
is  a  mysterious  power,  perfect  at  birth,  unerring,  unchangeable 
in  its  working,  and  radically  different  from  intelligence.  It 
has  given  the  term  a  more  precise  definition-  by  limiting  it 
in  various  ways,  e.g.,  from  reflex  action  and  habit  on  the  one 
hand  and  the  higher  mental  processes  on  the  other.  But 
comparative  psychology  has  not  materially  changed  the 
general  view  that  reason  is  confined  to  man.  And  the 
generally  accepted  position  is  that  the  observed  actions  of 
animals  may  be  explained  as  the  results  of  simple  associations. 
Some  experimentalists  have  found  material  facts  that  indi¬ 
cate  to  them  reasoning  ability  on  the  part  of  some  animals, 
but  this  conclusion  is  not  accepted  by  others.  Here  again, 
as  in  considering  the  subject  of  ideation,  it  is  necessary  to 
define  what  we  mean  by  the  term  reason.  This  word  has 
been  used  in  a  variety  of  ways  and  the  following  definitions 
include  the  most  important  of  the  meanings  that  have  been 
given  to  the  term.  A,  implied  reasoning  (Harris),  e.g.,  my 
recognition  of  yonder  horse;  B,  inference  from  particular  to 
particular  (James),  e.g.,  the  bird  which  finds  bread  upon  the 
window  one  morning  comes  back  the  next  morning;  C, 
adaptive  intelligence,  the  ability  to  adapt  to  our  purposes 
conditions  more  or  less  difficult  and  more  or  less  unfamiliar; 


52 


WILLIAM  SHEPHERD. 


D,  analogical  reasoning,  which  involves  construction  or 
creation,  e.g.,  to  reach  an  upper  window  I  utilize  a  ladder 
which  I  find;  E,  rational  thinking  (James);  F,  formal  or 
syllogistic  reasoning. 

That  the  higher  mammals  possess  the  ability  to  reason  in 
the  first  two  senses,  probably  no  comparative  psychologist 
will  deny,  although  the  explanation  of  the  process  may  differ. 
Implied  reason  is  probably  a  function  of  all  animals  and  the 
ability  to  infer  from  particular  to  particular  is  well  shown  in  all 
the  experiments  in  habit  production.  It  is  the  higher  level  of 
constructive  analogical  reasoning  concerning  which  there  is  dis¬ 
pute.  Has  the  animal  power  to  create  or  to  construct?  Hob- 
house  in  some  very  interestingexperiments,  claims  to  have  found 
satisfactory  evidence  of  the  presence  in  animals  of  this  class 
of  reasoning.  He  calls  the  mental  states  that  lead  to  this 
form  of  reasoning  articulate  ideas,  and  he  has  satisfied  him¬ 
self  that  these  are  present  in  some  monkeys  and  apes. 

With  the  purpose  of  confirming  the  work  of  Hobhouse  I 
made  experiments  on  three  monkeys  which  had  been  exten¬ 
sively  used  in  the  previously  described  work  on  discrimina¬ 
tion,  etc.,  and  with  which  I  found  it  most  easy  to  experiment. 

The  first  experiment  was  one  similar  to  the  box  and  the 
chair  experiments  of  Hobhouse.  Food  was  suspended  by  a 
string  from  a  long  pole  reaching  across  the  room,  too  high 
for  the  monkeys  to  reach  or  to  grasp  by  standing  or  by  jump¬ 
ing.  A  light  box  was  placed  near  the  point  of  suspension, 
but  sufficiently  far  away  that  the  animal  could  not  reach 
the  food  by  standing  upon  the  box.  Only  when  the  box  was 
moved  and  the  animal  climbed  upon  it  could  the  food  be 
secured  by  the  animal.  Each  of  the  three  monkeys  were 
given  three  trials,  in  each  of  which  five  minutes  were  allowed 
for  the  performance  of  the  act.  At  the  time  the  experiments 
were  made  the  animals  were  hungry  and  apparently  each 
watched  me  attentively  when  I  fastened  the  piece  of  banana 
to  the  end  of  the  string  and  suspended  it.  When  all  had 
been  arranged  the  animal  was  permitted  to  approach  the 
food  and  to  secure  it  if  possible.  The  actions  of  the  animals 
were  similar.  Sometimes  the  animal  tried  to  reach  the  food 


REASONING. 


S3 


by  jumping,  sometimes  after  the  unsuccessful  attempts  the 
animal  would  have  a  puzzled  look  and  finally  gave  up  attempt¬ 
ing  to  secure  the  food.  None  of  the  animals  seemed  to  notice 
the  box  and  none  made  the  attempt  to  use  it  as  a  means  of 
reaching  the  food.  In  their  actions  there  was  nothing  that 
I  could  interpret  as  a  sign  of  deliberation  or  reflection,  and 
in  this  experiment  I  was  unable  to  verify  the  results  of  Hob- 
house.  It  is  possible  that  the  box  appeared  too  heavy  for 
them  to  move,  but  I  did  not  notice  any  indication  that  it  had 
been  observed,  or  rather  observed  in  connection  with  the  food. 
That  the  box  was  not  too  heavy  was  shown  by  the  fact  that 
a  similar  and  equally  heavy  box  was  being  constantly  moved 
by  monkeys  in  a  large  adjoining  cage.  Failure  to  secure 
evidence  of  reasoning  in  this  experiment  may  have  been  due 
to  the  fact  that  I  did  not  continue  the  experiment  so  long  as 
did  Hobhouse. 

A  second  experiment  was  then  tried.  This  experiment 
has  been  described  in  connection  with  the  observations  on 
imitation,  and  the  apparatus  is  illustrated  on  page  42,  fig.  2. 
The  animal  had  to  move  a  long  pole,  pivoted  at  one  end, 
under  the  suspended  food  in  order  to  secure  the  food.  In 
all  the  experiments  of  this  kind  (three  for  each  of  the  three 
animals)  there  was  no  evidence  of  ability  to  grasp  the  situa¬ 
tion  and  to  solve  the  problem.  In  one  trial  an  animal  climbed 
upon  a  cage  which  was  near  and  jumped  from  it  to  the  food. 
In  general,  however,  each  animal  made  unsuccessful  attempts, 
most  of  them  directed  toward  the  food,  and  in  each  test 
finally  appeared  to  give  up  trying.  Two  months  later  one 
of  the  animals  (monkey  3)  was  again  given  three  trials  pre¬ 
vious  to  the  imitation  tests  and  failed. 

Adaptive  intelligence. 

Although  no  direct  evidence  of  analogical  reasoning  was 
obtained  in  the  tests  just  described,  other  experiments  on 
reasoning  gave  interesting  results.  Those  which  are  recorded 
in  this  section  deal  with  adaptive  intelligence,  the  reason  as 
defined  in  the  third  class. 


54 


WILLIAM  SHEPHERD. 


A  piece  of  twine  was  permitted  to  hang  in  front  of  and 
12  inches  away  from  the  cage,  beyond  the  reach  of  the 
longest  armed  animal  which  was  tested.  At  the  end  of  the 
twine  a  piece  of  banana  was  arranged;  a  thin  piece  of  wood 
was  pushed  through  the  banana  and  turned  so  that  one  end 
could  be  grasped  by  an  animal  in  the  cage.  By  grasping  and 
pulling  the  stick  inwards  the  food  was  secured.  All  the 
animals  were  tested  in  this  experiment.  The  results  with 
all  except  one  of  the  animals  were  similar,  and  a  description 
of  the  actions  of  one  will  suffice  to  indicate  the  whole.  As 
soon  as  the  banana  and  stick  were  arranged  monkey  6  put 
her  arm  through  the  wire  of  the  cage,  seized  the  end  of  the  stick, 
drew  it  toward  her  and  secured  the  banana.  This  experi¬ 
ment  was  repeated  a  number  of  times  and  in  all  there  was  a 
similar  immediate  characteristic  response.  There  appeared 
to  be  a  decided  adaptation  of  means  to  end.  No  efforts 
were  wasted  upon  random  movements.  It  did  not  appear 
that  any  preliminary  attempt  was  made  to  grasp  or  even  to 
reach  for  the  food,  but  there  was  an  immediate  movement 
toward  the  stick.  The  results  for  all  animals  are  given  in 
table  VIII,  in  which  is  shown  the  approximate  time  for  the 
performance  of  the  act  by  each  animal  in  each  trial.  The 
absence  of  hesitation,  the  direction  of  the  movement  away 
from  the  food  and  towards  the  stick,  and  the  promptness  with 
which  the  food  was  secured  speak  for  the  presence  of  adaptive 
intelligence  in  ten  of  the  monkeys.  It  would  seem  that  this 
is  almost  always  found  in  these  animals. 

In  this  test  the  results  with  monkey  5  were  decidedly 
different  from  those  with  the  other  animals,  in  that  he  failed  in 
the  trials  given  him.  Monkeys  i  and  4  had  considerable 
difficulty  in  getting  the  food  in  the  first  and  second  tests, 
but  there  was  no  gradual  acquisition  of  the  method  of  secur¬ 
ing  food  with  the  other  eight  animals.  The  times  for  solving 
the  problem  in  the  second  and  third  tests  were  approximately 
the  same  as  those  in  the  first  tests  for  monkeys  2,  6  and  10, 
and  there  was  not  much  difference  in  the  time  between  the 
first  and  the  later  tests  for  monkeys  3,  7,  8,  9  and  1 1.  Much, 
if  not  all,  the  difference  in  time  can  be  accounted  for  by  the 


REASONING. 


55 


better  adjustment  to  the  wire  netting  of  the  cage,  the  push¬ 
ing  of  the  hand  through  in  the  proper  place,  etc. 

TABLE  VIII. 

Adaptive  intelligence,  suspended  food  and  stick.  Three  or  six  trials  each  animal. 
Time  in  seconds;  f  =  failed. 


TRIALS  AND 
ANIMALS 

I 

2 

3 

4 

s 

6 

I 

60 

10 

3 

— 

— 

— 

2 

4 

3 

3 

— 

— 

— 

3 

20 

6 

9 

— 

— 

— • 

4 

los 

40 

I  I 

— 

— 

— 

5 

f. 

f. 

f. 

— 

— 

— 

6 

2 

I 

I 

— 

— 

— 

7 

6 

4 

3 

I 

I 

I 

8 

6 

4 

4 

3 

3 

3 

9 

5 

3 

3 

3 

4 

0 

10 

2 

I 

I 

I 

I 

I 

I  I 

5 

5 

3 

3 

3 

3 

A  second  test  of  the  presence  of  adaptive  intelligence  was 
made  as  follows:  A  light  wooden  lever  B,  18.5  inches  long 
was  attached  by  leather  hinges  at  one  end  to  a  board  A  which 
rested  upon  the  floor  The  hinge  of  the  lever  was  4  inches 
from  the  end  of  the  horizontal  board,  well  within  reach  of 
the  animals.  The  lever  was  inclined  at  an  angle  of  approxi¬ 
mately  45  degrees  from  the  horizontal,  and  could  be  moved 
forwards  in  a  vertical  plane.  Fig.  3  illustrates  the  apparatus 
in  relation  to  the  front  of  a  cage.  The  apparatus  was  placed 
outside  a  cage,  the  lower  end  of  the  lever  being  within,  the 
upper  being  beyond  the  reach  of  the  animal.  A  piece  of 
banana  or  other  food  was  placed  at  the  farther  end  of  the 
lever,  and  the  problem  for  the  animal  to  solve  was  how  to 
secure  the  food  which  was  beyond  direct  reach. 

Eleven  monkeys  were  tested  with  this  apparatus,  and  all 
with  the  exception  of  monkey  4  succeeded  in  the  first  test. 
In  the  first  test  the  animals  usually  took  a  longer  time  to  get 
the  food,  but  as  in  the  previous  experiment  this  delay  was 
largely  one  of  making  the  adjustment  of  hand  to  the  proper 
opening  in  the  wire  netting  and  not  to  attacking  the  apparatus 


$6 


WILLIAM  SHEPHERD. 


in  the  proper  manner.  In  the  case  of  monkey  4,  he  appeared 
frightened  at  the  time  of  the  first  trial  and  I  showed  him  that 
food  was  to  be  secured  by  moving  the  lever  against  the  cage 
and  permitting  him  to  secure  the  food.  In  the  succeeding 
trials  he  immediately  attacked  the  lever  and  qbtained  the 
food  in  the  same  manner  as  the  other  animals.  Monkey  9 
was  in  the  same  cage  as  monkey  8  when  the  latter  wasbeing 
tested  and  may  have  taken  the  opportunity  to  observe 
monkey  8.  That  she  performed  the  trick  may  have  been 
due  to  imitation,  but  I  have  credited  her  with  having  per¬ 
formed  it  in  the  same  way  as  the  other  animals.  It  is  reason¬ 
able  to  suppose  that  monkey  4  would  have  been  able  to 


Fig.  3.  Lever  apparatus  for  test  of  adaptive  intelligence  C,  leather  hinges;  B., 
lever;  D,  food. 


manipulate  the  apparatus  without  being  shown  if  sufficient 
time  had  been  allowed.  However,  in  whichever  way  it  be 
conceived  that  the  animal  performed  the  trick  we  have  a 
mental  something  very  much  like  imitation  or  like  adaptive 
intelligence.  In  many  of  the  experiments  the  animals  did 

TABLE  IX. 

Adaptive  intelligence,  lever  test.  Time  in  seconds;  f  —  failed. 


TRIALS  AND 

ANIMALS 

I 

2 

3 

I 

9 

4 

3 

2 

6 

4 

3 

3 

21 

2 

2 

4 

f 

6 

3 

REASONING. 


57 


not  use  both  hands  for  the  moving  of  the  lever,  but  one  hand 
for  the  lever  and  the  other  for  securing  the  food  when  the 
upper  part  of  the  lever  was  within  reach.  Table  IX  gives 
the  time  records  of  four  monkeys  in  this  experiment,  those 
for  the  other  animals  were  approximately  the  same  as  those 
noted  in  the  table,  although  no  accurate  measurement  by 
watch  was  taken. 

A  third  experiment  was  then  made.  A  stick  22  inches 
long,  with  I  inch  extending  into  the  cage  and  the  other  out¬ 
wards  from  the  cage  at  a  right  angle,  was  arranged  so  that  food 
could  be  secured  by  drawing  the  stick  lengthwise  into  the 
cage.  Ten  monkeys  were  tested  in  this  manner  and  all 
immediately  appeared  to  grasp  the  situation  for  they  pulled 
the  stick  and  secured  the  food  within  three  seconds.  In 
the  cases  when  the  food  was  dislodged  the  animals  immedi¬ 
ately  gave  up  the  stick  and  turned  to  the  food,  an  indication 
that  the  stick  had  been  recognized  as  a  means  of  obtaining 
the  food. 

During  the  progess  of  some  experiments  I  noticed  that 
monkey  7  attempted  at  one  time  to  pull  toward  his  cage  a 
small  tin  bucket  in  which  water  was  usually  carried  to  the 
animals  which  had  been  unintentionally  left  near  the  cage. 
From  this  hint  the  following  test  was  made  with  nine  of  the 
animals.  One  end  of  a  piece  of  twine,  i  yard  long,  was 
attached  to  the  bucket  and  the  other  end  was  left  lying  within 
the  cage.  The  bucket  was  placed  at  the  length  of  the  twine 
away  from  the  cage,  and  in  it  was  placed  a  piece  of  food. 
In  all  cases  the  animals  seized  the  twine  immediately,  drew 
the  bucket  toward  the  cage  and  seized  the  piece  of  .banana. 
Table  X  gives  the  times  for  monkeys  7  and  8.  These  times 
are  similar  to  those  of  the  other  animals. 


TABLE  x. 

Adaptive  intelligence,  pulling  bucket  inwards  by  means  of  twine.  Time  in  seconds. 


TRIALS  AND 
ANIMALS 

I 

2 

3 

4 

s 

6 

7 

8 

9 

10 

7 

6 

4 

3 

3 

4 

3 

3 

4 

3 

3 

8 

0 

3 

3 

2 

2 

3 

2 

2 

2 

3 

58 


WILLIAM  SHEPHERD. 


A  variation  of  the  problem  was  then  made.  The  end  of 
the  piece  of  twine  which  had  been  left  lying  loosely  within 
the  cage  was  tied  to  the  wire  netting  6  inches  from  the  end, 
leaving  that  amount  of  twine  within  the  cage.  In  this  test 
the  animal  had  to  reach  beyond  the  wire  netting,  seize  the 
twine  and  pull  the  bucket.  Seven  animals  were  tested  in 
this  way  by  an  assistant,  and  the  notes  are  not  so  full  as  I 
could  wish,  but  in  brief  the  results  are  as  follows: 

Monkey  i,  first  trial,  3  sec.;  average  for  10  trials,  3  sec. 

Monkey  2,  first  trial,  20  sec.;  average  for  other  9  trials,  3.5  sec. 
Monkey  3,  first  trial,  20  sec. ;  average  for  other  9  trials,  3.5  sec. 
Monkey  4,  first  trial,  5  sec. ;  average  for  10  trials,  3  sec. 

Monkey  6,  first  trial,  4  sec. ;  average  for  10  trials,  2  sec. 

Monkey  7,  first  trial  3  sec. ;  average  for  10  trials,  2  sec. 

Monkey  8,  first  trial,  120  sec.;  average  for  last  5  trials,  5.5  sec. 

In  the  case  of  the  animals  whose  actions  were  noted,  each 
pulled  at  the  short  free  end  of  the  twine  at  first,  but  soon 
reached  beyond  the  knot  and  pulled  the  bucket  inwards. 
This  was  done  by  some  of  the  animals,  notably  monkey  8, 
for  four  or  five  trials.  The  appreciation  of  the  knot  condi¬ 
tion  and  the  ability  to  deal  with  it  is  plainly  shown  by  the 
records  given  above. 

The  results  of  all  the  experiments  described  in  this  sec¬ 
tion  appear  to  speak  for  the  possession  by  monkeys  of  adap¬ 
tive  intelligence,  of  a  form  of  reasoning.  The  times  for  the 
performance  of  the  various  acts  are  fairly  conclusive,  but  in 
addition  the  appearances  of  the  animals,  their  actions,  etc., 
especially  during  the  first  trial  in  each  experiment  indicated 
an  understanding  of  the  problem.  There  was  no  fumbling 
with  the  apparatus,  no  appearance  of  learning  by  trial  and 
error,  but  there  was  instant  action  following  apparently 
instant  understanding  of  the  situation.  The  reactions  of 
the  monkeys  in  the  situations  provided  for  them  gave  diversi¬ 
fied  and  relatively  abundant  indications  of  the  presence  of 
practical  ideas  such  as  have  been  referred  to  in  the  section 
of  this  paper  dealing  with  ideation  (p.  4ofif.). 


MEMORY. 


59 


Memory. 

No  one  questions  the  fact  of  the  possession  by  animals  of 
a  sort  of  memory  for  acts  once  or  often  repeated.  Memory 
in  the  restricted  psychological  sense,  however,  has  been 
denied  to  be  present  in  animals  but  it  is  obviously  difficult, 
if  not  impossible,  to  determine  this.  The  nature  of  reten¬ 
tion  and  recall  are  matters  that  are  disputed,  but  that  animals 
have  an  organic  memory,  a  physiological  sort  of  memory, 
is  admitted.  This  memory  acts  well  for  practical  purposes 
and  may  therefore  be  called  practical  memory.  Whether 
or  not  this  be  merely  organic,  or  whether  or  not  animal 
memory  contains  a  representative  factor  must  be  left  for 
future  investigation. 

The  monkeys  observed  in  this  study  showed  good  ability 
of  recognition  and  retention,  of  the  practical  memory.  After 
the  completion  of  the  tests  on  visual  and  auditory  discrimina¬ 
tion  no  further  experiments  were  performed  with  the  appara¬ 
tus,  until  many  of  the  later  experiments  on  imitation,  ideation, 
and  reasoning  were  finished.  Memory  tests  were  then  made 
of  the  animals  previously  used  in  the  discrimination  tests 
with  the  following  results. 

Visual  discrimination  of  pink,  yellow  and  green  rice: 
monkey  i  took  the  green  ten  times,  took  the  pink  the  first 
trial  but  only  smelled  it,  and  on  the  fourth  trial  took  the 
yellow  after  the  green  but  dropped  it  almost  immediately; 
monkeys  2  and  8  took  only  green  and  paid  no  attention  to 
the  pink  and  yellow  rice;  monkeys  3  and  7  took  green  each 
trial,  and  in  the  first  trial  took  pink  after  the  green  and  smelled 
but  did  not  eat  it.  Auditory  discrimination  of  noises  after 
thirteen  days.  Monkeys  4  and  6  made  no  mistakes  in  ten 
trials  each. 

Lever  test  of  adaptive  intelligence.  Monkey  6,  after  130 
days,  showed  perfect  retention  in  four  trials;  monkeys  7 and 
8,  after  123  days,  were  also  perfect  in  four  trials. 


6o 


WILLIAM  SHEPHERD. 


General  Summary  and  Conclusions. 

I 

Monkeys  learn  to  discriminate  brightnesses,  but  take  a 
long  time  for  this  when  the  stimuli  have  not  a  direct  relation 
to  the  incentive  for  work;  only  a  few  trials  are  needed  when 
the  visual  qualities  are  a  part  of  the  objects  to  which  they 
naturally  pay  attention. 

Colors  are  discriminated  with  accuracy  and  rapidity  when 
the  colors  are  parts  of  the  food  (red,  pink,  yellow  and  green). 

Three  animals-  gave  clear  indications  of  the  discrimination 
of  different  degrees  of  noise,  and  also  learned  to  discriminate 
musical  tones. 

The  habits  are  formed  rapidly  if  there  be  the  double  incen¬ 
tive  of  pleasant  food  as  an  inducement  to  a  correct  response, 
and  of  an  unpleasant  stimulus  to  check  a  wrong  response. 

From  the  experiments  recorded  in  this  paper  it  appears 
that  monkeys  learn  to  inhibit  recently  formed  habits  of 
action  with  facility. 

As  far  as  the  evidenc-e  goes,  in  regard  to  both  the  formation 
and  the  inhibition  of  habits  monkeys  are  superior  to  raccoons 
and  far  superior  to  dogs,  cats,  elephants,  otters  and  other 
mammals  which  have  been  experimented  with. 

Monkeys  have  a  practical  memory;  they  appear  to  show  a 
good  degree  of  retention ;  the  representative  function  in  mem¬ 
ory  is  an  unknown  quantity. 

Of  the  higher  powers  of  mind  the  monkey  has  only  rudi¬ 
ments.  He  has  a  something  which  corresponds  in  function 
to  ideas  of  a  low  order  and  which  serves  practical  purposes. 
This  something  we  call,  with  Hobhouse,  practical  ideas. 

Two  of  the  monkeys  learned  by  imitation,  but  six  others 
gave  no  indication  of  imitation  ability.  It  may  be  said  that 
while  monkeys  may  learn  by  imitation  to  a  limited  extent, 
imitation  as  involving  ideation  is  a  small  factor  in  their 
ordinary  learning  process. 

All  the  tested  animals  appeared  to  reach  a  generalized  mode 
of  action  in  dealing  with  problems  but  there  seemed  to  be  no 
evidence  of  true  general  notions.  They  have  an  adaptive 
intelligence,  a  lower  form  of  reason,  or  a  mental  state  inferior 
to  true  reason. 


BIBLIOGRAPHY. 


6l 


Bibliography. 

(1)  Aristotle:  Natural  History  of  Animals. 

(2)  Watson,  J.  B.:  Some  Experiments  bearing  upon  Color  Vision  in 
Monkeys.  Journ.  Compar.  Neurol,  and  Psychol.,  vol.  19,  no.  i,  1909. 

(3)  Watson,  J.  B.:  Psychol.  Bull.,  vol.  6,  p.  295,  1909. 

(4)  Yerkes,  R.  M.:  The  Dancing  Mouse.  New  York,  1907. 

(5)  Kalischer,  0:  Eine  neue  Horpriifungsmethode  bei  Hunden  u.  s. 
w.,  Sitz.  d.  k.  p.  Akad.  d.  Wiss.,  vol.  10,  Berlin  1907. 

(6)  Selionyi,  G.  P. :  Contributions  to  the  Study  of  the  Reactions  of  the 
Dog  to  Auditory  Stimuli.  St.  Petersburg,  1907. 

(7)  Morgan,  C.  L.:  Animal  Behavior,  London,  1900. 

(8)  Thorndike,  E.  L.:  Animal  Intelligence,  Psychol.  Rev.  Monog. 
Siippl.,  vol.  2,  no.  4,  1898. 

(9)  Thorndike,  E.  L.:  The  Mental  Life  of  the  Monkeys.  Psychol. 
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BF21.P96v.12 

A  study  of  sensory  control  in  the  rat, 
Princeton  Theological  Seminary-Speer  Library 


1  1012  00008  4774 


